The Magnavox is SD only. I have the DHG also. There is little difference in PQ between those two. The Sony does support DD5.1 though. I have my 515H set to send in 1080P only.
Bits are bits but some devices use more than others. The Mag does not run all the time. You can buy a new DHG remote and clean the fan. I've had four Sonys and none show any age issues. I have three now since I gave one to my mother.