That amp is magical, I have only just replaced mine in the main system after 25 years of pleasure. What pre-amp will you be using or did I miss something? Mine sounded very fine with a Creek passive although the Quad 34 was pretty good too.
Its a pity space is a problem as the 20 sounds really good with my Quad ESL57s. I also ran it into Kef 101s which were pretty nice too. You can get those for very little when they come up, unlike the LS35a which, to my ears at least, don't sound quite as 'musical' ie when they are playing I tend to hop up and down less in time to the music. I would think a system based on the Leak/Kefs would suit your choice of music quite well. Wouldn't suit headbangers of course.
As ever, the problem with buying second hand / eBay is that you can't listen extensively before you buy which is the only real way to buy hi-fi.
Shouldn't go wrong with the little Kefs though.