HH, welcome. The advice from the Denon rep seems a bit nonsensical and possibly biased toward the newer, more expensive, model. All amplifiers are "stable"(if that's supposed to mean that they don't shut down)with a 4 ohm load unless they're driven too loud and too long. The M80s, whose average impedance over the entire frequency range is on the order of 6 ohms and which are slightly above average in sensitivity, are fairly easy to drive and can provide safe listening levels with lesser receivers than the 4310. If you want the 4311 because of some new feature, fine, but don't buy into some line about it somehow being more "stable".
