[gblaue]

They’re something else going on. The max rms voltage out of the amplifier would be 8.5Vrms if it was in its engineering flat mode. That would be about 24Vp-p. With the vehicle eq, maybe 7-7.5Vrms max.Audio Source specs the speaker level input at 40V max. I would assume that it is p-p. They don’t spec what its input impedance is. I’d expect it to on the order of 10kOhm. Some Japanese manufacturers like to drive down to 300 Ohms. The Bose amp will not care about driving anything. It shouldn’t trip the short protection on the Bose outputs unless the load goes less than .75 Ohms.

The reason that you only 3.3Vrms on your hand held meter is because it samples very slow, compared to audio being sampled at 48khz, then averages. You need an oscilloscope with it set to max hold.