I have a Raven Tour rather than the Sport so you’ll have to decide for yourself how much, if any, of my experience is relevent.
I’d normally use my lighter derailleur tourer for Audax. The Raven has done a few, a couple of winter ones on mucky lanes, some where I carried camping gear to the start and one when the other bike had mechanical problems. There are pluses and minuses in having a Rohloff. If you’re riding on your own you can take full advantage of the ease of gear changing, being able to change half way up a hill rather than at the bottom and changing up for a short downhill where you wouldn’t bother changing chainrings. If you’re in a group you miss out on those advantages, it can be frustrating. The other big advantage is how forgiving it is, no fluffed gear changes and getting stuck on the wrong gear on hills and junctions, really appreciated towards the end of a long ride. On the minus side, I sometimes find the 13% gap between gears a bit much, in the most used gears on my derailleur bike the gaps are around 8%. Again this doesn’t really matter if you’re riding on your own, you choose whether to put a bit more effort in and go a bit faster or take the easy option and lose a bit of speed. When I’m in a group I’m often looking for a gear between. I’ve never used drop bars on a Raven, but experience with bar end and downtube shifters on other bikes convinces me that if I don’t have to move my hand to operate the gears I’m more likely to use them.
You can of course Audax on any bike, as gets demonstrated at every ride I’ve been on. There’s also a wide variety of Audax, both in terms of distances and topography. On yesterdays flatish 200 in bright sunshine the ideal bike would have been a thoroughbred road bike. I’m doing one in Wales next month that’s almost entirely on Sustrans tracks, where my Raven will be in its element. I did my first season on a mid range hybrid and neither of my bikes was bought specifically for Audax. Unless you’re one of the lucky few who can afford a shed full of quality bikes, what else you’re going to use it for should maybe have a bigger influence.