SX-550 update - R channel distortion solved w/Q-4/6/8/10/12 replaced w/overkill parts (50W MJEs, KSC1120, etc.). L channel AUX problem was in MIC jack. 2.2M chassis resistor replaced, and 3 lamps replaced. Vinyl is removed and ready for refinish. Tuner aligned tightly in AM/FM/MPX and I'm listening to the Brewers losing on WTMJ from my basement on only the factory loopstick. She's working great now.