i think that receiver should do fine, but if you hear any distortion or clipping you might need a bit more power...you room is very simialr to mine.
I use an emtiv xpa-5 200 watts/channel (unlike the denon which s only rated 2 channels driven) and I notice a big improvement in headroom and sound dynamics...I do suggest you go with an external amp but if the funds dont allow it...you should be fine for now