I think you're on the right track - particularly with the separate amp for the sub. That gives you so much more ability to balance the bass/sub-bass levels relative to the higher frequency sound. I can't tell you how many stereos I've seen with boxes full of subwoofers and a single big amp, where the owner had to crank so much bass out of the head unit to make it listenable that all the mid-bass went away too. We call those Hiss-Boom systems -- 5KHz and up, and 90Hz and down with nothing in between.
I'm currently running the same 4" MB Quart co-axials in my dash that you are, plus a pair of 6" MB Quarts in the doors and a 5.25" MB Quart center channel speaker, all off of a PPI 100 watt amplifier; then in the back I have a single 10" Orion dual voice coil speaker running full range - not as a subwoofer - on a separate PPI 50 watt amplifier. I added individual pots so I could attenuate the three mid-size MB Quarts independently - I can control both the amount and location of my mid-bass that way. No equalizers, no crossovers, no speaker boxes, all simple, all totally stealth, and if I can believe the competition judges, exceptionally high sound quality.
Be sure to tell us how it works out, particularly any differences (better/worse) when you switch from your CD player to the empeg.
tanstaafl.
"There Ain't No Such Thing As A Free Lunch"
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"There Ain't No Such Thing As A Free Lunch"