i bought a 98 avant 2.8

wrecked it in a month, and just got it back from the body shop yesterday

i have a couple of questions

1. it comes with the concert stereo, i want to put in a different head unit, is there an adaptor so i can use the stock speakers? its hard to find one.
2. has anyone used lltek for parts? they have an exhaust system in there cat. that looks promising, just wondering if it is worth it.

i know im new but would really appreciate the help

the reason i bought an audi in the first place was mainly because of info i found on this website.