While the Class D Crown XLS 2000 has a lot of watts for $500 (375W/ch @ 8 ohm, 650W @ 4 ohm), outside of PA use, the main home audio use by far is for passive subwoofers.
A combo that might keep you and the Salk SongTower RTs happy for more than a few years is the Parasound 2100 preamplifier mated with the Parasound 2125 amplifier (Class AB, 125W/ch @ 8 ohm, 200W/ch @ 4 ohm).
There is one of each available used on Audiogon right now, and at the price it would be hard to go wrong. The Parasound 2100 preamp for $435 and the Parasound 2125 amp for $425 makes an $860 combo that would be hard to beat for sound, features and price.
Steve