Does anyone know if the AntMiner S5 supports #xnsub?
Not yet, but we are working with Bitmain to provide #xnsub support for AntMiner S5 as well as AntMiner S4 . It should be available very soon, we'll post here when it's ready.
Actually. Surprisingly yes. It does work at least with the current firmware from the website. Just add #xsub to the end of the stratum line and viola.