need advice from audio pros
The monsoon external amp sends full freq range to the mids in the doors and hatch. Pontiac tweeters are driven from the HU integrated amp, also sent full freq range but there is a small in-line RC HPF blister in the wire. The monsoon external amp applies an LPF of unknown freq (probably around 250 Hz) to the sail panel midbass channels.
So without knowing all the details of what you did, I would advise you to make sure the little RC filters are protecting the tweeters, and make sure you didn't load the mids and tweets in parallel so they lower the impedance/load seen by the monsoon external amp. If you upgrade to an aftermarket amp, use the external crossover modules that should have been included with your component speakers.
I would not put anything full range behind the front seat as anything more than a fill effect from small hatch speakers will draw the soundstage backward. If you don't care about that and just want more volume coming at you from all directions, then go for it.
With most components sets, you would normally not use an external crossover module with the stock monsoon amp because the power loss is too great to justify the better filtering with a relatively weak amp driving them. Normally, you're better off taking advantage of the additional power the Pontiac setup provides, since it makes use of the available HU power, but provides no filtering on the mid-cone. If you go to a more powerful aftermarket amp, then it's better to use the higher order filter that came with the component set.
Since your higher order crossover is integral (by design) to the mid-cones, you can't bypass it on the Hybrid mid-cone. So, in order to keep the volume levels proportional, your best option is what you did, run everything off the monsoon amp. You might suffer some volume loss, but it sounds like you were more concerned with sound quality anyways.


