KEF Cresta 2 replacements?

I've currently got an Arcam Alpha 3 amp (40WPC) running a pair of Cresta 2s.

Has anyone any ideas on speakers to replace them with, preferably ones I'm
liable to pick up second hand. Floorstander VS Bookshelf doesn't really
matter. What I'm after is better bass - the Alphas don't seem to produce
good low end bass, which is hardly surprising considering the size of the
box and the drivers. Preferably something that isn't a bass reflex design as
they're not straight in front of a wall. I might be better off with a sub,
but I rarely hear of anyone using them for music rather than films except
for Don Pearce's post just now.