Guru reqd for intermittent sound

[ccarinae]

I've tried everything except outside help, my sound output works but output drops after a while for no apparent reason.

I've;
updated drivers,
checked every option in the driver setup,
replaced the mobo,
scoured the web (to no avail),
consulted the manual (unbelievable!).

I'm using the onboard sound for 5.1 digital out to my amp. It goes out via single coax rca cable.

Sound is configured through Dolby Home Theatre software for 5.1 and works nicely and sounds great.

The problem is this, after some time, say 20 - 30 minutes it starts to drop sound. Short drops at first (1-3 secs) and as time goes on longer and longer pauses until it is mostly silent (1-15 mins outages). The amp says there's no signal (a high-end Marantz that's been serviced and verified as normal).

All sound producing software is equally affected, games (DX and Windows), WMP, although iTunes seems to last 60 minutes before dropping.

The only thing that I've found that solves the problem is a reboot and then it is just back to square one.

Hardware is as follows;
Gigabyte EP45-DS4P (Realtek ALC889A sound)
Intel E8500CPU
3GB RAM 800MHz
nVidia GTX260 900MB
2x 250GB + 1 500GB drive (all SATA)

Windows response can be slow at times, although I've shutdown most unncessary services, including indexing. These's no correlation between this and sound drops.

Any takers???