Apparently it can't be done, Petey B. Steve says I should do the upgrade via the serial RS232 cable but my wife's Compaq Presario 700 laptop has no serial output. At this point I seem to be stuck.

Frankly I never noticed any "big volume difference between Stereo, Bypass, Upsample", and I have (had!) no reason to use 5 channel stereo anyway. I hope I will hear some stereo again soon.