Jazzmt,
I want to thank you so much for your time and effort. I'm telling you, there is some serious money to be made here. You need a website and merchant account. You should be able to set this up cheap with SBC small business plan or something along these lines. You could be up and running in a 3 days. I'm sure if you got the word out there on enough Subaru websites you could mint a small fortune.
This is not just for Legacys but for the whole subaru lineup. Hell, subaru should be working directly with you to add this as an accessory. But alas, I doubt they would as they seem to be clueless that people actually want MP3 and aux in capability.
I wish you all the best in with this project. I'll be buying one in the near future.