[MrNice]

Test another distro. You seem to be having issue with OE, try Raspbmc.

So, you mean that OE is not good for playing multichannel music file.
I'd be glad to get popcornmix and MilhouseVH opinion.

BTW, I've yet to see a pi running XBMC on any overclock, extreme or otherwise, running hot enough to need heatsinks.

Even if the CPU temperature reach 78 C as it did, with the heatsink? (measured with OE)

[popcornmix]

Even if the CPU temperature reach 78 C as it did, with the heatsink? (measured with OE)

What's the ambient temperature?
If the Pi in a case without ventilation?
Is the Pi on top of other equipment that runs hot (like a receiver)?

[popcornmix]

Test another distro. You seem to be having issue with OE, try Raspbmc.

So, you mean that OE is not good for playing multichannel music file.
I'd be glad to get popcornmix and MilhouseVH opinion.

I would be surprised if raspbmc/xbian runs better than openelec, but it could be worth trying.

[MrNice]

What's the ambient temperature?
If the Pi in a case without ventilation?
Is the Pi on top of other equipment that runs hot (like a receiver)?

Ambient temp is 14/17 C not more.
RPi is on a furniture aside AVR. No heat is coming from AVR
RPi is in a clear box with 3.5mm diameter holes every 9mm. Around 48 holes on the top + some on side.

I'll try over-clocking without cover box.

@popcornmix
Are there any log/info/setup you want to try to found out the issue?