I'd start by upgrading the AVR first to one that will support additional external amplifiers.
Accessories4less sell refurbished Onkyo TX-NR709 receivers for $450. You would most-likely get a more powerful amp section in the receiver along with the pre-outs, updated audio formats, and Audyssey room correction.
I really don't see anything in your speaker setup that would really take advantage of anything that supplies more than 200 watts/channel. You can look at Audiogon for stereo amps in the 150 to 200 watt/channel or maybe look at the Emotiva XPA series.
HD-DVD = 94
Blu-Ray = 120 ( 24 Warner red2blu )