Any way to adjust gain on Ford factory Sony amp?

I just installed a Pioneer AVIC-Z110 in my wife's 2009 Ford Flex, which has the factory amplified Sony system. I used the Pac-Audio RP4-FD11 to retain the factory amp and steering wheel controls. I have a couple of issues, they may be related... I think the factory amp gain is high because I can only go to about 9-10 in the HU before it starts to distort. This volume level is also pretty loud at this setting. Second, there is some low level static/white noise that I can hear whenever I change sources, radio seek, change track, etc.

I had this HU installed in another one of my cars, so Im pretty sure the deck is fine.

Any advice you guys have is appreciated.