I would suggest any of the upper-tier Parasound amps from the 2-channel HCA series: HCA-3500, HCA-2200II, HCA-1500 (in descending order of wattage/power). Between 10 and 15 years old; should range in price, used, from ~$800 (HCA-3500) to ~$350 (HCA-1500). They're all rated for 4 ohms; the 2200II is rated down to 2 ohms. The 3500 and 2200II are probably the ones you want for those speakers.
Recommendations for a "summer" amp?
Living in a hot southern climate I'm considering acquiring a 2nd amplifier for summertime use as a backup to my Pass Labs amp which runs quite warm. Solid state, cool-running, fairly recent vintage (don't want to invest in service) with a used price somewhere below $800. I had a good candidate in storage but I gave it to my brother so I need some recommendations. My system is comprised of an ARC tube pre and B&W Matrix 800 series speakers.