Current audax machines below:
Singular Osprey which I absolutely love and use for most things, it's supremely comfy, and deceptively fast! I'm running 28s under the guards but could probably squeeze 30 or 32s with wider guards. Only changes to pic are it's got a SP hub on the front now and using an old Suntour VX rear derailleur instead of the Ultegra one in the pic after it 'migrated' to my wife's bike to enable use of a bigger cassette for her.
The Bianchi blue Mercian is my second option, a bit heavier, 32/35mm tyres, slightly different gearing, just as comfy as the Singular but not quite as sprightly. I tend to use when exploring new routes at slower pace or if I know the roads are going to be particularly awful. Frame came from here 2nd hand an despite looking tiny it has a very low BB which drops the whole bike (hence short HT) and it is just as long as the purple Merican below and longer in the TT than the Singular above!
The purple Mercian is SS and used for shorter rides and some club runs/exploring rides, it actually has laods of clearance but a poor choice of narrow guards is currently limiting it to 'big 23s/small 25s' and until I get round to changing the guards it'll stay that way. It does currently have a dynamo and Edelux on it too though but they were fitted after the pic.
I have a lovely Bontrager Road-Lite too for fair weather use but it's currently in bits pending a rebuild!