Hi Jeff K,
There's no risk from phantom power if you connect the L1 Compact Line Out or T1 Master or Aux Outputs using the 1/4 inch (6.3mm) Tip-Ring-Sleeve cable to a mixer 1/4 inch (6.3 mm) jack. As you know, phantom power is only (optionally) applied to XLR inputs.
If you are working with a house system, and specify you are providing a balanced line-level source, you should be fine. We hope whoever is running the house system will know how to connect things to correctly to a line level input (that should not have phantom power).
Of course, there is the possibility someone could
- Convert the 1/4 inch (6.3 mm) Tip-Ring-Sleeve connection to XLR
- Connect that to a microphone input on a mixer
- Turn on the phantom power
If you want to avoid the issue entirely, use a 1/4 (6.3mm) Tip-Sleeve cable when connecting to an unknown external system.
If the input provided is XLR then you could use a passive DI between the L1 Compact or ToneMatch mixer.
1/4 inch (6.3mm) Tip Sleeve connection (short cable) to the DI. XLR out from the DI to the house system. This would eliminate any risk of phantom power coming back to the Bose equipment.