But what's funny is that it is designed to work with the factory amplifiers in place (which have no gain adjustment). They even make an adapter to do the same thing if you want to replace the factory amps with aftermarket ones so it isn't designed for that.

Just odd.....maybe something has changed on the 09's but all the part numbers I have referenced seems to be the same for 2007-2008. Oddly, Crutchfield says this part doesn't work for my truck even it is a 2007-2008 but PAC says it does. Who knows...

 

The Infinity system is an odd one to say the least.
I have the Infinity in my truck and the friggin amps are mounted on the speakers in the front doors.
So when I wanted to upgrade my speakers, I had to break the magnets off the original speakers to get the amps off, make an aluminum plate to use as a heat sink, mount the amps to the plates, lengthen the wires, mount the plates in the doors where they wouldn't interfere with the window regulators, and then install the new speakers.
What a pain to say the least, so nothing would surprise me on any Infinity designed system.

 

Yeah, I'm pretty happy just using the line-level converter for my sub amp. It worked in the past but this time I just wanted to do it the "right" way.

I've put custom stereos in about 20+ of my past cars. But once I got a Mustang that had the Mach 460 premium sound I soon learned it was easier to just gut the entire system and start from scratch on "premium" systems.