Just a quick update... Got the Audison Voce Component speakers fitted along with an Audison SR4 amp, Bit One Processor and Hertz Hi Energy 10" sub (in a box in the boot), along with the front doors covered in Dynamat. The amp's under a false floor in the boot, and the Bit One's currently under the passenger seat.
Results are very pleasing. So good that I'm listening to music I'm really familiar with, and all the time thinking to myself "I didn't realise that part had strings in it" or "the drummer was a bit flaky with his timing in the middle section, there" etc. etc. Acoustic guitar, vocals and drums (the "tappety tap" ones) are really crystal clear and incredibly sharp and precise. And the sub, whilst I don't like it taking up boot space, does do a worthwhile job. If there's a "Bump Bump Bump" accompaniment, it's like the B is provided from the fronts and the "ump" is catered for by the sub. Except it's just there, surrounding you. And when LCD Soundsytems' "Disco Infiltrator" is played loud it's like there's a wave of bass rolling from front to back, straight through you. Made me laugh.
Negatives? I'm getting more fussy with the quality of recording (I swear I hear a chair move during Vaughan Williams' The Lark Ascending) and the production of some recordings is simply flat and one dimensional (you can't make a silk purse etc even if you remaster Band on the Run...). There's also a little interference with radio reception (but that'll get sorted). Plus the BitOne is, as suggested, a hobbyists choice requiring a lot of tinkering and tuning. Maybe I should have gone for the MS-8 Snoopy... And then there's the cost. What started as a search to spend £300 or so to get a nice sound to match the Dynaudio I never ordered and possibly the B&W system in a colleagues new Jag turned into a comfortably north of £1500 "Maybe I'll do a little overtime this month" bill, and now I've been bitten I'm sure it won't be the end...
Would I do it again? Sure! I'm enjoying music like I haven't in twenty years, and even looking forward to long journeys up and down the M6.
Thanks again for the advice, audiophiles!