Cliff (KU4GW),

I agree fully with using DATA-U mode vs. SSB since it bypasses any SSB mic equalisation that may be dialled into the 991A, giving a flatter audio response up to at least 3 kHz.  Something else I'd suggest if you want to control the 991A in parallel with running WSJTx is to use FLRig as the middleware.  After installing FLRig and verifying that it has control of the 991A, change the "radio" in WSJTx to "FLRig".  I've been operating this way for a long time and like the ability to change 991A settings on the fly without disturbing WSJTx.

73,,
Hugo, ve3ktn.