Are you SURE about that!
That Pioneer uses Digital amplification (Class-D). Most digital amps use BTL outputs. Meaning the negative terminals are NOT ground! And are not connected to one another. So shorting them together or ground will send the amp into protection. Or worse if the protection circuit doesn't respond well enough, burn the amp up.

This also becomes important when using cheap volume controls on digital amps. Some cheap volume controls have the negatives tied together, sending the amp into protection when used.
One brand name that still does this is Russound. Their volume controls are the same ones they have produced since the early 90's and are common ground. Even thou they have digital amps with non-common ground in their lineup. Just stupid.
The one time I saw this burn up an amp, was with a NetStreams keypad (which used a digital amp). Installing company used a cheap volume control for a bathroom, split with the bedroom. Keypad kept shutting off and eventually burned up. Original company could never figure it out and eventually stop responding to the customer. I was called and fixed it pretty quickly.

[Note]:
I don't know if that Pioneer uses common ground or not. But being it uses Class-D amplification, it's a good bet that the grounds are lifted. A quick check with the multimeter would easily verify.