Hi Martin,
The Multimedia Setup facility for choosing default devices in Warp 4 has never worked correctly for me. Lars' USB audio drivers add a new page to the 'System' tab that allows choosing the default device that does work. You could try adding the USB audio drivers and use that to choose the default.
If you want to remove the SoundBlaster, you can also edit the MMPM2.INI file by removing entries for the SoundBlaster, but it can be tricky. Once edited, you have to <ctrl><alt><del> to reboot (NOT a regular reboot or shutdown) to make changes stick. Be aware that improper editing of MMPM2.INI could prevent the computer from booting, so be sure to have a copy of the original MMPM2.INI file in case it goes wrong...
Regards,