Also, between most recievers, the amount of power is not really a big deal, so for yourself I wouldn't worry too much as the more power isn't going to make a huge audible difference. Choose which you like the best.
The 50W/ch HK will give you 5X50 with all 5 channels driven simultaneously. The 90W/ch Denon may give you less than 5X90. The 90W/ch Denon will have more powerful amplifiers because each channel will be able to output 90W. The HK should give you more than 50W with only 2 channel driven simultaneously, may be 65WX2 but not much more than that. This may not be a fair comparison, but I am just trying to answer your question.
Shiu it's pretty accurate but I found that most companies seem to not be anywhere near accurate with there low-end recievers but as they go up in price, the more reliable they seem to be.
Chris, you made a good point, glad to see that while you are still promoting Hk (me too, for their sound quality), you now seem more tolerant of other makes "higher end" models. HK does seem to be able to make the whole line up, i.e. 1XX through 6XX sound reasonably similar. As you move up the line, you get more features, power and better build quality. The same cannot be said about many other mass market manufacturers.