Just installed my USASPEC, DF-TOY interface, sounds pretty good, but lost the use of my 6-Disc indash cd changer. I'm still debating the loss of the changer but since I bought my 4-Runner I haven't used the CD-Player much, so right now seems like a good trade off. The nice thing about USASPEC, is that it allows for 2xStereo inputs, so I can always add a disc man, or I-POD later, in addition to my carputer. And as I plan to pipe MP3's throughout the car, the loss of the CD Changer isn't looking that bad right now.
Checkout the attached image. Right now I'm working on the mainboard and getting the Computer Installed.