you'll have to tell us a little bit more. what have you tried, how do you set up the output? like did you stick to whatever default output(which one?) and just let waves NX ask you if you want to use it, or did you set waves NX as default output straight in windows? (shouldn't change anything but better know exactly what you're doing).
the buffer values in NX were all working for me as long as I wouldn't also chain plenty of DSPs in foobar. I imagine you've tried the different buffer values in NX and nothing changed?
the digital level also never was an issue for me even maxed out, but just in case did you try lowering the output on your player to check if the distortions were going away at some point?
as far as I know it's not really possible to force a resolution value NX doesn't want. the player or whatever would just be rejected and play no sound at all, or win mixer would convert to whatever it is NX wants.(I think)
I don't know the creative X7, but maybe try to set it by default at a different sample rate, and of course if there are any sort of DSP integrated like is often the case with creative gears, make sure they're OFF at least as long as you're troubleshooting.