In the stock Monsoon system, the rear speakers are driven by a left and right channel for the mid range speaker cones, and a subwoofer channel that drives both side's large cone. If you're replacing the OEM speakers with aftermarket, you've got choices - use the mids, use the subs, or tie both together. I tried all three and wasn't happy with the results. I think that the Monsoon amp has internal crossovers tuned for the OEM speakers.
The same goes for the front. The two 6.25 speakers and the front door tweeters are both the same channels with crossover applied. What I never did figure out was the dash speaker.
I scrapped it all in mine and replaced the Monsoon amp with a Pioneer four channel unit.
I believe your amp is taking a dump.
