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Deliberated picking up a sram red etap kit for one bike but noticed it doesn't come with brakes. Also ultegra brakes are pretty good already so happy to keep those if they will work with shifters.
Also have durace crankset but expect that would be okay with sram mechs and shifters. Anybody run this combo.
I run an ultegra rear brake with sram TT brake levers without any problem. Friend has ultegra levers and sram brakes so I can't imagine you'd have any major problem (not that I've tried your combo and it might be not quite optimal cable pull  amounts according to sram/shim)
As long as you're not talking hydraulics, they should work. They won't be optimal, but they'll stop you.