I wouldn't mess with the wiring on the MPSS-4. I sure would like both of my HU's to be on all the time, but I think it may get funky when both signals hit the MPSS-4. I think that it powers down one HU to make the source switching easier. Hell, maybe is's super lame and just uses power cycling as a "source switch". Either way, I've learned to live with it and love it.