Alright guys I'm new to SSA and Fi. I'm Ramin, i live in Cali. I'm paying my friend about 100 a week for a Bl 12" w/ cooling, a Nine.1 Amp, and a custom 2.4cuft box tuned to 32hz. (i'm paying 640 altogether) He had the setup for about 2 weeks, and now decided he's gonna get the bl 18. So he's selling me his new setup. Well firstly, is there anything i should change about that setup. I could for example sell that amp and get a new one. Secondly, i'm not the best with car audio. My friends help me with most of the installation etc. I know a decent amount though. The setup will be going in a 07 Audi A4, and a couple friends have been telling me that i'd need a new head unit because the sub needs to be connected to the speakers cuz they cant be connected to the oem head unit or something. Problem with that is I paid quite a bit for navigation etc, so new head unit is out of the question. I got a few suggestions. Such as OEM integration (soundcontrol for example) or connecting the stock amp to the fi sub and to the nine.1 amp. I don't remember how exactly. Anyway. Help would be much appreciated and i'm sorry about the long post.