That's a great setup, if only the Pi had optical out for sound I'd use it for the same thing. I'm still struggling to get it as a torrent server![]()
I have a Sony surround system and the HDMI pass's from the Pi to the Amp to the TV. The CEC TV signals also pass through. No need for Optical out.
I would take your RPi to a friends or family members house and try on a none VM connection. VM has some weird throttle rules for P2P traffic based on network load, time of day for the sub 30Meg netwrok.
Do you have another device you could try to torrent on. Or try the bag of peas cooling method and see if it's the Pi over heating and slowing down to stay in thermal limits.