New system amp/speaker advice

I am replacing factory system in my 03 Ford Excursion. I am looking at the new Alpine 9861 HU, Infinity Kappa 50.7cs components (85 watts RMS) in the front doors and 1 or 2 Infinity Reference 1040w subs in the rear cargo doors. Components and sub(s) would be powered by a Profile AP1040 80W x 4 amp. There are also 4 rear speakers tied together. My question is I was initially looking at 4 6x8 Infinity Kappa 682.7cf (100 watts RMS) run from an amp but was recommended that just run off HU for rear fill. The HU only puts out 18 watts RMS per channel so I thought a couple sets of 5 1/4" Infinity kappa 52.7i (55 watts RMS) might be a better choice. Now, should I run the 4 rear speakers from the HU or get a 5 or 6 channel amp? I don't want to get into 2 amps. I'm not trying to blow the windows out, just want good clean sound. Any help/opinions would be appreciated. Thanks.

I hear alot of talk about rear fill.  If you are looking for sound quality then amping the rear speakrs is the way to go.  Do so though with a good amp and a good pair of speakers.  czesc

sounds like your running a serious setup coming. I would suggest hooking up every speaker to an amp somehow. get a nice 4 channel amp that can handle all of the combined power, and obviously a subwoofer amplifier. my friend has an excursion for towing his race car, and wow, what a serious interior, that thing should sound awesome once you get some good speakers and amps in it. and i dont know why youd want to get rid of the stock head unit and everything, unless my friends is a top of the line option, yours has controlls for it for the back passengers, and on the steering wheel, and headphone outputs? if it is the same one you should keep it, and just run line out converters to the amplifiers, then a bunch of wires to them speakers. good luck with it, should be awesome when complete.99 Blazer LT.   Yellow Top. Big 3. Infinity Kappa Speakers All Around. Jensen CD/DVD flip out. 2 Infinity Kappa Perfect 12DVQs powered by a Alpine PDX600.1 (in one custom box, building a FG box)

Thanks for the input guys. I didn't want to run two amps, but probably a good idea. I am trying to keep all this on the down low, don't want the wife to know I am getting all this gear! I think she can deal with a new HU, but wouldn't appreciate good quality speakers, amps and subs. Will have to tuck those amps away somewhere! BTW, I don't have the premium sound in my Excursion, does have controls and headphone in back, but no steering wheel controls, etc.. The main reason I want the new Alpine HU is for the direct ipod connectivity and sat radio. The only way to get ipod in now is rf converter, sounds terrible! The deck has built in changer so no changer input or line-in to tap into. Any recommendations for a descent mono amp? I am looking at one or two Infinity Reference 1040w 10" 4-ohm subwoofers to put in my rear cargo doors (with a custom enclosure). Thanks again!