disconnect the fan on the mg800 , leave the case top open and dont use an internal hard drive. I have no lockups and I have 2 running for over 2 years. They are on all the time and I stream from my server. Both fans are disconnected and I have the top open an inch and have a screen to keep the dust out.
or try a pch or the upcoming player
http://www.nixeus.com/ I have tested the fusion out and its trying to fix all the issues the mg800 along with a new processor for high bit rate mkvs and a better UI. The Fusion will be my next player.