Hi Dan,
I'm not sure the B&K reference 70 you are looking at does actually do all the latest codecs (DTS Master Audio and Dolby TrueHD do not seem to be present). It may be touted an extremely 'clean' unit in terms of sound quality but really, what does that mean? There are so many variables that can be treated first to get accurate sound such as room acoustics that no matter how clean your sources are, if your room acoustics are bad, you really are missing out on your 'good' sound. This is where the newer processors potentially have an advantage if utilised correctly - room correction.
So anyway, I'd upgrade and move on

If you want a 'Preamp' I can strongly recommend the Integra/Onkyo range as I am using an Integra DHC-9.9 myself and have found it to be a truly excellent unit. Properly calibrated with the Audyssey MultiEQ XT Pro installer's kit, it really is excellent value for money (should be well under $2k US now as it is on runout sales atm). The new models are the Integra DHC-80.1 and the Onkyo PR-SC5507p (same unit but currently without the Audyssey Pro enabled I believe) and they retail for about $2399. You can probably again pick them up for a bit below $2k right now. Going this path, you can continue to use your B&K 5 channel Amp till you figure out you want more 'grunt'

It still probably won't go to waste as the new Integra/Onkyo has 9.2 channels (all with balanced XLR outputs btw) so you'll still need to get another 2 stereo amps or a 5 or even 6 channel amp (hey you may want to run passive subs?) Anyway, if that is not enough, very soon, you may even want to run a full Audyssey DSX setup which is 11.x channels (the new Denon 4810 has 3 subouts and does 11.3 supposedly and has 9 channels of amplification on it)
Another thing, if you haven't heard the new audio on Bluray, you really are missing out

Lossless formats are AMAZING. Also, many Blurays seem to be mastered much better than their DVD counterparts on both Audio and Video. And IF you are going to add another 2 speakers for 7.1, try adding it for front WIDTH channels over rear channels. It is meant to be a much bigger improvement.
BTW, if you look at your other post regarding HDMI to component, I may have a possible solution