I wouldn't worry too much about driving 4ohm speakers with the Denon. I have a Denon AVR 3300 (105W/ch) connected to a pair of Legacy Focus mains and Silver Screen center (4ohm, 94db efficienct). I've never had any problems driving them. I believe my volume control ranges between -30 to +30 and I normally listen at -17which is plenty loud for music or home theater. The receiver has never shutdown on me. Another thing to consider is you have a sub. Since bass takes most of the power to produce, having a sub takes a lot of strain off the receiver. By allowing the sub to carry most of the load your main speakers will only require a percentage of the receiver's power to drive the highs and mid-range. Where you may have needed 30-45W/ch to drive a full-range channel, with the sub the demand may drop to 20-25w/ch. This would be very simple for a good quality receiver like the Denon.