Since the 4x6 are fairly weak, and my 6x9 have about the same RMS as my subs (120 for speakers, 100 for subs), is it feasible/worthwhile to get an amp that puts out 4x100 RMS and use it on the speakers and subs and either a baby amp for the front or just run the fronts off of the head?

Kinda new to the car audio thing, so I'm not sure what kind of problems this might create, if it's even doable.

 

Sure! You can get a 100x4 amplifier, run the 6x9's and subs all off it,a dn run the front speakers off the HU...no problem!

Good luck!