I have a HTR-5890 that is being used as the "main stereo" (not the big stereo, the one that plays through the house) with 2 mission m35i tower speakers. I've pushed this thing near its max volume, and it hasn't distorted a bit!

(one comment about these speakers though, you can turn the volume up to massive levels, yet the speaker cones never "move" thats how good the port and design of the case are!)