Not an Audaxer here either, but I did build an Audax/Winter/Night-ride bike and went Custom 853 from Rourke. I was looking for almost the ultimate do-it all road bike for long rides and local faster club runs.
Going this route allowed me to have a frame that fits my particular shape (could never get standard frames quite right for long distances), allowed DT shifters, 3 bottle cages, odd brazings for racks, cables and other paraphernalia, equiped with hub-dynamo lighting, 28mm tyres and guards. I opted for 853 forks which are stiff making the bike feel nice and lively when stripped-back but not too bad either over 200 plus miles. Carbon is cheaper but you can't add braize-ons.
Gearing is currently 48/38/28 with an 11-27T 9 speed rear which when the chain wears-out will be replaced with a 32 or 34T rear. There are some ferocious steep hills around Folkestone and Dover...and I'm not getting any younger!
All in all I'm chuffed with the result. It's not super light due to componantry/lighting, Brooks saddle etc. But it's a fast lively ride that will take medium loading such as a large fully stuffed saddle-bag and bar-bag really well (hostel/CC touring, lightweight camping). Fully loaded with Rack and Panniers works, but is nowhere near as happy and stableas a proper tourer would be.
It's unique, idiosyncratic and does exactly what I wanted!