I have the box that the retail version of the Aztech Sound Galaxy NXII, which had a lot of the compatability and features of the NX Pro 16 Bit cards, came in still, but no manual or drivers.

Yea it seems if it has NX in the name there is chance it has Covox support. The other thing is look a LPT emulation jumper.

The NX II wasnt 16 bit but rather more on par with the Sound Blaster Pro 2.0. But it does have DSS, Covox, CPM and other compatability. I always just used Sound Blaster or Ad Lib for games and had no problems with it. I never used some of the more essoteric and lessor compatability modes.