I spent quite a bit of time going back and forth between the systems when I was considering the 63 instead of a 65. I was torn, and was somewhat happy to have the stereo decision taken out of my hands when I opted for the 65.
I'm an audio nut, having put more into my home listening systems than into cars, but it was still a tough decision between the two systems. The B&O is clearly superior in terms of accuracy of sound, frequency extension, ability to create an actual soundstage (something I've not previously heard from a car system), and all of the usual audiophile checklist items. BUT, it only comes alive as you approach reference volumes. At lower volumes it tends to sound a bit thin, almost tinny. Boosting bass and mid range can partially address this, but then it sounds sloppy when you turn it up.
The HK system, while not as accurate, has a pleasing well-rounded sound at moderate volume levels, and does a very credible job at higher volume levels as well.
In my opinion the HK could be a better choice if you listen mostly to modern popular music, frequently drive with a passenger (and want to be able to talk to that passenger), or if you don't like to listen at 92+ decibels. Conversely, if you listen to a lot of classical or jazz and like to play back at live volume levels then the B&O is far and away the better option. If you're in both camps like me then I don't know what to advise
