If weight is not a problem and you absolutely need a new amp then what do you guys think about RMX5050?
You can find it new on google product finder for $1550 and up.
From what I read here the XTI 4002 gets bad sounding results from every one connecting it to the 728 although I heard a few sales people recommend this combo, don't know why.
I own one 4002 and use it happily on 4 tops.
A pair of 6002 are supposed to do the job (Kevin from the crown forum recommends it) but I don't have first hand experience with it.
You can find allot of used gear that will fit your power needs and budget, such as QSC PL9.0 or a couple of Crest 8002 that would easily do the job, but your best bet is to get a used i-Tech like ray and tim said