Pre-amp tripping breaker on power amp

I have a luxman l-480 integated. When I use a Quicksilver line stage into the power amp-in jacks, it periodically trips a breaker and the amp geos dead for about 20-40 seconds. It always comes back on, and does this evan when the volume is "off".
The pre-out on the luxman has unusually low gain for an active. Lower than a passive with 1.8 mv going into it.
What would possibly cause a circuit to shut down, evan with "0" gain into it? (note the Quicksilver has it's attenuater before the gain stage)
try verifying your interconnect cabling integrity - there may be a bad connection or loose shield at a jack. Sounds like the amp is going into protect mode. Similar things can happen, with separates, if you leave the power amp energized while plugging/unplugging unbalanced interconnect cables; you hear a loud buzzing sound & may even blow a tweeter.
Sounds like excess DC-offset in the line stage to me. Any competent tech can test for this. Good thing your amp has a protection circuit.

Best of luck,
Did your Luxman run hot before it shut down. If it did, it might be in some sort of oscillation which overdrove the amp and triggered the thermal protection circuit.