Help w/Amp Install

[timneff]

Just getting into car audio. I am not ready to change out the head unit but wanted better sound. I changed out all four factory speakers. This helped but I needed more base. I cut the wiring to the back speakers and installed a 10" subwoofer and a 500 watt amplifier. I used the high-level inputs on the amp. This amp has a RCA throughput so I connected a 200 watt amp using RCA wires to drive the rear speakers. Once everything was connected I turned on the HU but noticed a significant decrease in the subwoofer volume. When I disconnect the RCA cables from the second amp the sub really kicks in. I can't figure out what the problem could be.Can I split the speaker wire from the head unit and run them into each amp seperately? Should I get a line-level convertor to convert the high-level to RCA? I have a spare BOSS AVA-CR200 2 channel electronic crossover. Would you recommend using this? Any help is greatly appreciated.

[mu_ohio]

Your install really confuses me, but you should run the line converter into your rear speaker amp. From that full range amp I would run my rcas to the sub amp and turn the amp to low pass.