So windows does something, and you blame your soundblaster?One thing I've seen with my Z is Windows has a "really" annoying habit of changing my default output device to my NVIDIA HDMI connection for whatever reason. Make sure the default (and preferred) output device is "Speakers (Sound Blaster ZxR)". I recommend doing this through Control Panel->Sound so you can manually set the preferred output device.
The fact you are getting audio at boot means the sound card is connected correctly, and it's likely audio is getting re-routed somewhere else after startup. It's also possible (though unlikely) that some programs may be overriding the audio output device; for testing just use the built in audio output utility from the Sound Blaster Pro Studio.
i think with the new nvidia driver you click custom and then you can untick the audio.You got me. I totally miss that. In the old days, when I install an older driver of nvidia, they allow me the option of NOT to install the other stuff, such as their audio, so I just grab the basic driver back a no. of yr. ago in the old PC.
This new PC, when I download the nvidia latest driver, it doesn't give me that option. I totally forgot they screw around w/ my audio too.
Coincidentally, today I finish off putting together this new PC, w/ a good part of it : scratch build