Hi Doug,
I've sold lots of AVR520 with the M80TiSe with no problems yet. The AVR520 has a very robust power supply. The M80TiSe is an 'easy' four ohm load too.
I would suggest checking your speakerwire connections for short circuits at the speaker and amp ends. If one strand of wire is touching the opposite, the '520 will tolerate that at very low levels but as soon as you turn it up, then the protection circuit kicks in. Hopefully you find that's all it is and no servicing is required.