L1 Model II with T1 Sound Drop Outs
A quick review of four POSSIBLE causes of audio cutting out follows. That will help us determine what is going on.
Bass Module Cable
If there is a non-Bose B1/B2 cable, OR if the B1/B2 cable has a defective, loose connection, audio can intermittently mute. It may happen with loud music because the speaker will be vibrating and shake the loose connection. This will sound like a clean muting of all audio for a second or so. There will be no visual indication.
Fixable by tightening the screws in the connector.
For more details see: Sound Fading In and Out
Power Issues
Very low, out-of spec, AC power (less than ~105 VAC on a 120V system, or less than around ~215 V on a 230 V system. The manual states 110 and 220 for good measure) coupled with high signal level. This can be caused by a low power source, or one where the outlets are a very long distance from the electrical panel, extra equipment on the same electrical branch, power sags or dropouts, long or multiple extension cords, or small gauge extension cords.
In this case, loud music increases the current draw, and the voltage drop over the extension cord will lower the voltage enough to cause a reset of the ToneMatch Mixer[1], or the L1 Model II Power Stand.
If the ToneMatch Mixer[1] resets, the LEDs (input trim level, mute LEDs) will turn off. The LCD display will remain lit, but be blank until the unit restarts. The L1 Model II Power Stand can reset but it does not show on the indicators.
In either case, the answer is to ensure the power supply is solid and dedicated to the audio equipment, and to have as short cords as possible with large wires. Also be aware that separate wall outlets may still be on the same breaker.
If there are intermittent voltage sags or outages in your area (as there are in parts of Florida, for example), it is possible that some equipment that does not use a lot of power (like mixers) will continue to operate, and equipment requiring high power, like amplifiers, may not be able to produce audio.
Those outages can happen any time, but are less likely to repeat, or unlikely to happen only at loud parts of the music.
More: Power Considerations
Overheating
If the L1 Model II Power Stand overheats, it may shut down. This can happen under direct sunlight outdoors when the temperature exceeds the maximum operating temperature. Check the access to the fan is clear (opening at the front of the power stand) and that legs are on a flat sturdy surface. If the power stand is on a carpet, it may sink down and obscure the vents on the bottom.
Defective Unit
Defective units: If the items above are not the cause, then either the ToneMatch Mixer[1] or power stand may be defective, and you should contact customer service.