This is the kind of thinking that led me down a rather long road...I did a little write up in this thread: https://www.allfordmustangs.com/forum...-inside-4.html
FYI, I found that the ford system works great, except when adding aftermarket speakers without proper amplification and sound processing. The OEM Head Unit's esp will decrease bass as you increase volume, and the general sound processing leaves a lot to be desired. Keep in mind the system was built with crappy speakers as the foundation. It really does make a huge difference to do it right. and I highly recommend adding sound processing. If you are going to put that much effort and money into your sound system, you might as well think about doing a complete job
with re: to the clean sweep - If I remember correctly you need their signal summing interface also, so that'll add extra cost. And then there's the cost of tuning the system....
A better option for you might be the new audison bit ten, or even the JBL ms 8, either of which you can tune yourself.And I have read that they perform excellently. I went a slightly different route by getting a high quality full system amp with sound processing already built-in, and had it professionally tuned(~$75) and the sound is fantastic
I probably won't ever put the GT500 mufflers on my car, but I can still hear that rumbling sound while I have the tunes cranked up - as the old song says, I'm in love with my car.