Welcome along Joel. If you get your questionnaire back to Tim and get full access to the site there is a lot of information regarding upgrades to the Hi Line system. Most replacement units come from Sean (aka Radioguy) on the 75/ZT OC forum here:

http://75andzt.com/index.php?route=common/home

What car have you got? What are the last three digits of your VIN? Any photos?

Nich.