Updating my last posting regarding some issues with the sound on my Pismo, I can report that a software reinstall solved the problem of my USB turntable communicating with the computer.
The remaining problem is something that is constant whenever my computer is on—static coming from the speakers. Mixed in with the static is a subtle rhythmic beep. It doesn't rise above the level of background noise, so it doesn't really interfere with playback of media, but is certainly obvious when there is no other playback.
In addition, use of the internal mic and built in speakers is impossible without excruciating feedback. The mic works fine with headphones. Perhaps this is normal.
As problems go, it's fairly small—unless it means that my AC/Sound board is on its way out.