bnew, not everyone wants to use their speakers in a living room with a small amp. If Jrock ever wants to use his Imperial as a DJ or for sound reinforcement he needs a big amp. Also, not all big amps sound bad, even in the first watt. I don't know about his amp, but I use a PA amp on my home system and it sounds very good at any sound level and few amps of any kind could touch the signal to noise level. I can also put the speakers out on the deck and turn them up as loud as I need to and still have plenty of headroom.
Jrock, don't even think about buying premade boxes and removing the drivers. That won't save you any money unless you get them cheap used. You should also know that decent pro coaxials are very expensive. Drivers with a 2" exit HF unit will sound better, almost without exception, compared to 1" exit horns. The bargains are more likely to be found using standard woofers and putting horns on top of the box.
Whether you go coax or not, the crossover point and the transition from woofer to tweeter will be a challenge. If you want to spend a lot of money you might consider this:
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=294-686Bet it sounds real nice.
There are few 15" coaxials on the market. Let us know if you find one you really like.
Here's a 15" driver that looks to me like it was designed for the Decware Imperial:
http://www.speakerrepair.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=01-...Reasonably priced too.
Eminence does make a line of coaxials including a 15" (the Beta series) but the motor doesn't look beefy enough for horn loading. If you choose Eminence coaxials remember they don't come with the HF driver or crossover.
Someone on this forum used Eminence drivers in an Imperial and found a largish peak around 2k hz. If you plan to use EQ or crossover below that won't be a problem but something to consider. (Jim, was that you?)
Good luck on the project and keep us updated. Thanks!