It's an interesting description with that kit. "Tired" I mean. The CD63 was hardly a shrinking violet in either the standard or KI versions. The 752 (is this the pre-Freedom version with the mesh dome tweeter? If so, it is a good one to hold on to) is anything but dull, but it will tend towards a lean presentation if the partnering kit is short on bass too. The 8000s I don't know too well, but I hear Audiolab can be quite bright, or at least, nearer to that end of the spectrum.
Is there a chance you might have a little too much brightness and less bass? A couple of thoughts here...I'd hang on to the speakers for now, as they work well and DO have a good bass presence if the other kit has that to offer. £700 will get you a decent new amp, or a possibly very good used model. Hell, half that will get you some good used kit.
The speakers don't need a huge amount to power them, anything from 25-150wpc, so a little off the wall, but give a thought to the Icon Audio Stereo 25 (
http://www.iconaudio.co.uk/Stereo25.html), which you can get for £500 direct, plus they'll throw in a valve upgrade to EL34s into the bargain. Good reviews from WHF and Hi Fi World to name but two. I'd shortlist for sure.
Maybe a Rotel pre/power combo? Used will get you something like the RC03/RB03 set-up, new might see you get the 1072 integrated, that might do it. A NAD pre/power could be a good option. I think you might have a similar sonic preference to mine; liking the detail in the presentation, but the warmth to go with it wouldn't go amiss. Perhaps some of these options might help.
Oh, one other, ahead of the above, Musical Fidelity V-DAC. £130. Not necessarily better than the existing CD63 but possibly so and easily as good as.
Budget used effort - NAD 3020A. £60 should get you one, it's got bang for the buck, great bass, decent treble and a lovely midrange. Can't push it too hard though as it gets unruly when the dial gets to 10 o'clock, but it'll drive those Missions with ease and better than some. The trade off is a slightly reduced soundstage, but I hear good things about parterning it with a Linn LK100 power amp. You'd have enough change to take your good lady out to dinner in a good place and help keep the peace into the bargain...!