I spent hours on the Denon biamp experiment...using zone 3 to get more punch to my lows...it sounded awful. Tonal imbalance. and the hum was annoying, especially in my small room, i could hear it very easily. People say to go to +2 on zone 3 volume. why even bother? You can't hear the bass increase until about +7 or +8 and you get hum at that level. Yeah you get more bass, but at the expense of degrading sound quality to ALL of your speakers, just not the fronts. You also can't use the 6.1 channel...The amps in the zone 2 and zone 3 are not as good as the main zone amp..that's why you get a "tonal imbalance"...So many people tried to get rid of the hum...I tried a power conditioner, isolation transformer, tried taking the ground off my wires like someone suggested...nothing helped. people who say they don't have the hum with this "ghetto biamping" method have not hooked it up correctly.
Save yourself some time. Buy a power amp, used like I did, and power your lows with that. I paid $200 for my NAD 2200.
But...if you can handle sound degradation for a bit more bass, go ahead. i wasn't prepared to make that sacrifice.