If someone can help me out please, there are a lot of posts about this but not very clear.

I fitted a RNS-E in my Audi A4 B6 and i have two amplifiers, one for door speakers and one for the bass(really common setup). I had a top model Kenwood before the RNS-E and the sound was amazing. Really something. Now that i installed RNS-E sound if really not good, especially the bass. We connected the amplifiers to line out from RNS-E(front to front and rear to rear & bass amp).
Now since i know RNS-E has only 2V preout amps and this is obviously too low i want to install line output converters to get better voltage or preouts for the amps. On what should i connect them to? Should i connect them to wires going to the speaker from my original amp(not bose, regular one)? Because if i wanted to connect them directly to RNS-E, there is only front speakers and all the signals would be coming out of that one source which i think is stupid because of navigation and stuff.

Can someone please clarify how can i get three normal preouts using line out converters?

Thanks a lot! :)