loginfailed - what type of sound card are you using?
I ask, because I've been using a P2140, had a P1900 before. At one point (NOT when I first started using the P1900) I got the same symptoms as you in terms of it not holding standby. I battled with it on and off for 5 months, and at this point, I'm 99% positive it is my onboard sound (Realtek HD Audio on my Aopen i945gtt-vfa).
So, I'm curious: which sound card are you using?