The first thing that happened is no sound coming from the left front speaker. No matter what configuration I put it in 5.1, 4 etc it still is the same. I even went back to the card and verified the innstallation, and still the same problem.
When doing the speaker test in 5.1 the sound that comes out is a very distorted low bass from the woofer, not the left front speaker as it should be. The rest of the speakers work fine. My speakers are Polk audio 130's.
I was thinking it may be the installation of the card , possibly the hook up of the cables...
Im not sure, sounds like you covered all the possibles. I have read though that alot of speaker manufactures were having trouble with 5.1 when it came out. Im not running 5.1 yet, havent found a set that really jumped out at me. Sorry I couldn't be more help.