I was working with an upper end Yamaha that was paired with 4 ohm speakers. The Yamaha doesn't have a "4 ohm" setting, but it does have both 8 ohm and 6 ohm settings. The speakers just did not sound good on the 8 ohm setting and sounded much better under the 6 ohm setting. Most of these low impedance speaker problems have to do with the amplifier power supply and amp circuit. Some of these just don't have enough brute force in the power supply to be able to push enough current for low impedance speakers. I suspect these receivers are switching a 2 or 4 ohm resistor into the output load of the speaker binding posts, therefore increasing the load a bit higher so that the amp power supply / board has an easier time driving the speaker load. Like Erik said, the result is a little less power output because you are now splitting power between a 2/4 ohm resister and the actual speaker, but the sound quality should improve.
Imhififan's suggestion of an outboard amplifier would solve your problems. You could even look into a beefy 3 channel amp if you wanted, to drive your entire front stage. In HT/movies, the center channel is almost the most important speaker.
Imhififan's suggestion of an outboard amplifier would solve your problems. You could even look into a beefy 3 channel amp if you wanted, to drive your entire front stage. In HT/movies, the center channel is almost the most important speaker.