Hiya Stevie,
Indeed, I have replaced the roof antenna with an AM/FM/DAB combo - twice in a fortnight! (As it'd be an upgrade on the scrappy glass-mount thing included with the DAB receiver we got, we thought we'd have a go with a cheapy eBay one - the old adage applies - buy cheap, buy twice.)
It's by no means an horrendous job, but there's one bit which isn't for the faint-hearted, and one bit which isn't for the large-armed...
The main issue is the hole in the roof Honda made. More accurately described as a slot. It's ~12mm wide by ~25mm long, which is just too small for most of the antennas on the market. There's a possible exception in a Connects2 model, which some retailers describe as requiring an "approx 11mm mounting hole", but it's not mentioned in manufacturer specs, and Connects2 never replied to my ticket. In the end we bought a Kinetic DRA-6001 from dabonwheels, partly because they're great people who respond to email and offer a no-nonsense 45-day money back guarantee, partly because I found out it's a re-manufacture of a Bosch/Blaupunkt design I'd used years ago, and found to have excellent performance.
The fleabay cheapo one and the Kinetic one both require a ~14mm mounting hole. (The Kinetic one is supplied with o-rings for 14.8mm & 19mm holes, more on that in a moment.)
So, we took a diamond file to the hole(!) and widened it out by about a mil for about 14mm of the 25mm sides - effectively giving us a 14mm x 14mm square opening roughly in the centre of the slot. It sounds a bit of a scary bodge but it didn't take long to do, and with a spot of paint to seal the edge, or even just liberal application of grease under the new antenna (which you should do anyway), it'll be sealed just fine.
The bit about being not large-armed relates to doing the job with minimal (i.e. less than the book says!) trim removal. The Honda manual says to change the antenna, the headliner must come down; to do that requires removal of the C-pillar/quarter-light trim, and there's about a dozen trim clips on that, most of which will break if you do. We did it just by reaching between headliner/trims at the tailgate opening. The trickiest bit is disconnecting the stock antenna's cable tails from the main run, the connector for which is behind the C-pillar/quarter-light trim on the passenger (UK, RHD) side.
Assuming I haven't scared you off... Here's the drill...
Remove the boot light (trim tool/small flat head in notches on the edge of the lens, two cross head screws under it).
Remove the two plastic trims on two anchor points to the left and right of the roof (pop off pretty easily - lever at edges).
Remove the cover for the ISOFIX anchor toward the centre of the roof (probably easier to do when you've pull the headliner down a little - the 'inside' part is just clipped into a securing frame on the back of the headliner).
Slip the headliner out of the rubber tailgate seal and start to pull it down a bit, there's a trim clip near the boot light which you can carefully pop-out without breaking to get a bit more access. (There may be one on the other side too, I can't remember for certain and most of the rooting-about is done toward the passenger side.)
Before you remove the antenna from the roof, you'll probably want to disconnect the tails from the main cable run (because if you can't get to it there's no point carrying on). As I say, that's behind the large trim covering the C-pillar/around the quarter-light, probably about a third/half way along the window (of course the cables off the antenna base will lead you to it, a torch helps see it). We got to it by popping-out one trim clip near the tailgate opening toward the top of the trim - you'll know the one as soon as you start pulling at it - luckily I've got computer operator's arms(!) so I could just about get to the connector. The connector is held with another one (possibly for the curtain airbag) in a clip which is trim-clipped into the bodywork behind the plastic trim. The best thing you can do is get hold of the whole lot and pop it out of the bodywork so you can bring it back far enough to get a good grip of it do undo the connector on the antenna cables.
That's the fiddliest part done. Next, removing the antenna base itself...
Be brave - you might feel like you're going to permanently crease the headliner by shoving your arms in, but ours went back fine - you should be able to feel for the wiring going to the base of the antenna through a hole in the inner roof skin, and the nut/bolt which secures it. IIRC it's a 17mm nut, I got a 3/8 drive ratchet with a universal joint and short socket on it without much fuss; it wasn't tight.
Once you've wiggled it all out, you're ready to install the new antenna. As I say, we just decided to open out the slot a bit to get our antenna of choice installed. As I mentioned, the Kinetic one we bought comes with two o-rings, and you are supposed to use one or the other; actually we found neither to be that great a fit with the opened-just-enough new hole, but when we offered it up without either it sat down perfectly - and of course as this is a modified long slot which extends forward and aft of the antenna's bolt, the o-rings wouldn't really have sealed it anyway.
The next minor pain in the backside comes from how the nut fits on the new antenna - on both of the ones we played with, the wiring is supposed to come out of the slot in the bolt above the securing nut (there's a slotted collar on the top side to allow this); you may manage it, but because of the shape/size of the aperture in the inner skin, we gave up doing it that way after throwing a few F's at it. Ours is fixed with the wiring coming straight out of the bottom of the bolt - the only issue doing it this way is that you'll have to tighten the nut with an open (we used an adjustable) spanner rather than a socket.
Before tightening everything up, I forced a bit of general purpose equipment wire into the gap between the collar on it and the nut proper, to give me an additional/definite earth connection for the antenna - the underside of the outer skin looks like it's got at least some paint on it, so I wasn't sure we'd get a brilliant earth through the nut in contact with it. (The boot light is earthed on one of its mounting screws, I just looped the other end of my belt-and-braces earth strap around that - works beautifully.)
The last thing to do up top is put a load of grease on the outside of the roof (between it and the antenna base) to make sure it's all watertight. Tip: put loads on; if it's oozing out of the edges when you tighten everything up, great - it's sealed, just wipe off the excess. Spanner-in, nut nice and tight.
Now it's just a case of routing the wires to the head unit. A wire coat-hanger (or simiar) will be your friend
We went down behind the C-pillar trim, and picked it up behind a handy little vent which pops-out with a bit of squeezing & pulling, pictured below:
Again with your trusty wire-poker-thingy, head toward the front of the car, and you can fish it out under the trim just behind the seat back (there's a notch for a trim tool but if you've got dry hands squeezing/wiggling/pulling will pop it off). With the seat flipped forward, pop off the trim below the squab/on top of the door-jam, pass the connector(s) under the plastic frame/behind the seatbelt anchor and then tuck the wires under. When you get to the B-pillar you'll need your pokey-thing again to get around the front belt tensioner and gubbins (there's a panel on the base of the B-pillar trim, over the belt tensioner/anchor, slide it upwards to remove it; it makes life easier). From there it's pretty plain sailing; the trim over the door-jam by the front passenger seat just lifts off and you can route the wiring under it. The next one along (covering the base of the A-pillar by the passenger's feet) only needs a bit of wiggling to get enough access or remove completely according to taste. I tucked the wires from there along the bottom edge of the glove box (there's a useful gap you can get into with a bit more wiggling around the hinges), and then you're at the centre console.
(Trims as described in order, N.B. red wire in last pic shows the bunch (that's ant power))
Job done. Generally get ~90 DAB stations, including regional for the next regions along (Merseyside/GM/North Wales) with good reception in all but the most adverse conditions:
N.B. The mast on the DRA-6001 model is a decent amount longer than stock (doesn't foul the tailgate). They do a version with a shorter (23cm) mast - DRA-6003, but the 6001 gives best performance across all radio bands.
See also: fakey OEM roof bars - Amazon bargain

[About £65 delivered.]
Sorry for the mammoth post; I hope it's useful!
All the best,
Rob.
P.S. If by any amazing chance you're in range of Lancashire, I can give you a lift doing the job if you like.