M4A78LT-M-LE 5.1 audio problems

Hello!

I am experiencing some issues with Asus M4A78LT-M-LE motherboard.
It has 8 channel integrated audio, which supports HDMI mode as well as analogous connection (Line-In / Mic jacks are used in this case).

Audio drivers VIA High Definition Audio v6.0.1.7900 are installed on my Win 7 Pro x64 system. VIA HD Audio Deck configuration tool is included in drivers.

I have 5.1 analogous speaker system connected to appropriate jacks and system is configured to 6-channel mode. HD Audio Deck as well as Windows native playback configuration allows to test each channel independently. Tests confirm that channels are working as they should.

But... after several minutes (random) of audio inactivity (e.g. Internet browsing, writing) system turns off all other channels except fronts (FL and FR). Configuration remains the same, but rear and center/SW channels are like "muted" (no sound output). The only way to get channels alive is to switch to 2-channel mode and then back to 6-channel mode.

Do anybody have experienced something similar on Asus mainboards? Or, probably, with VIA drivers? I'll be grateful for any advice.

Thanks!