So the question to Fosi is, should it work with a high level sub connection to V3 Mono? I connect the cable to the + (red) terminal on one of the monoblocks.
I tried to connect a BK XXLS400 sub with high level to V3 mono, but I didn't get any sound. I tried to connect the sub to a Class AB amp with high level, then it works. The input impedance on the high level on the sub is 100K Ohms.