Hello Steven,
Honestly, I'd say go for it. I love HK receivers. They are packed with instantaneous, high current power. I bet that 50 watts per channel is probably near the low end of what that receiver can deliver. HK isn't really known for fudging specs like some receiver companies, so 50 watts per channel is probably a pretty modest spec. And as I said the power is super high current which is more important in driving your speakers then a high wattage # anyways.
And it should sound amazing with our speakers. HK's couple very well. I know that the 4B's have a 84 dB sensitivity which may seem a tad low, but one must keep in mind that for most of the listening that you do, you are only using a small fraction of what your receiver can deliver. The HK will really have the headroom to deliver if you need it. Man I love me some HK...
So again, in short, I say go for it!
David Bolt
Aperion Audio Guru
www.aperionaudio.com