Hard to point you directly at any one instance, but trawl a few threads either here or on other boards and you will come across instances where Denon's ratings are questioned. As said, I've the forerunner to both the AVRX4000 and the 4100 and this uses the exact same PSU and I'd have to agree with the sentiment that these receivers aren't the best when it comes to their power output. I'd not slate the AVRX4100, but I would advise caution if wanting to power low impedance speakers to reference level in a moderately large room. As I said, this is D&M's weak spot not only with the AVRX4100, but also in relation to the SR7009. THey've been slated for this for a few years now so maybe that's why the sudden appearance of the 4ohm rating despite there not actually being a different PSU employed? The rating itself is an odd one, given that it is stated on the reverse of the receiver, but not stated on Denon's own site within the receiver's specs?