Bro i have same problem with u and same ideal which is using AMP + PC + LCD.

Mine even worst

I use HDMI output to LCD , then OUTPUT my LCD audio jack to Speaker.

No sound at all. I know i need to set my Audio setting in PC to HIMI AUDIO. Dont know y i cant select the HDMID AUDIO. Maybe i need to reinstall my Sound Drive.

Beside, If i use my Dell LAPTOP studio 15. Same hardware setup. The laptop automaticly detect the HDMI. Because my Laptop using windows7.
And my PC using winXP.