A BeoSystem 3 would be your best bet, if you wish to have B&O integration throughout. If you want to consider an option to that, then I'm of the "You don't say?" school when it comes to claimed excellence for various surround-sound processors/amps.
The Parasound comment above, about setting the BL5s to neutral, isn't really necessary. We've had Dave Moulton here earlier stating that there is a factory calibration reset, but this just sets the speakers to interact with a room in Struer, and isn't a "neutral" setting. The Parasound would just measure the output from the speaker-array, and then just calibrate each speaker's signal accordingly, no matter what the BL5s were set to.
If the BL5s were wildly off-target (which is unlikely, as they are adapted to the room), then you might get issues.
I have found that the acoustic lenses of the BL5s, and their exquisite resolution, make a centre speaker unnecessary in my case. I'm using a non-B&O processor which allows me to send the Low Frequency and centre-channel information to the front speakers.
Remember that your B&O speakers have in-built amplifiers. All you want to send them is a properly resolved and defined signal, and they'll handle the rest. Surround-Amps are judged on their ability to drive speakers, which will not be an issue in your case.
When I purchased that processor, the dealer knew I had been considering getting one from Classé and when I bought the one I now have, he said that I wouldn't be coming back for the Classé. And he was right - my Cambridge 540R surround processor does an excellent job with standard surround, whether from DVDs, AppleTV or other sources. Of course, it's way too cheap to be taken seriously by the home theatre cognoscenti.
However, my next processor should be capable of handling multi-channel, high resolution audio - and the 540R isn't. Look for that if you're going non-B&O in your choice of processor.