Hi Turek -- I'm pretty familiar with the K250. In the absence of info on personal tastes, I can only offer general comments. So here goes:
The 250 can drive practically anything and I've rarely (if ever) felt there was a "mismatch" with the different brands of speakers I've heard driven by it. If anything, it was just the inherent "musical character" of the speaker coming out; one either liked the speaker in question, or didn't...
So it all boils down to:
a) the volume limits imposed by your room size and treatment...
b) yr tastes in reproduced sound, i.e. which speakers reproduce what you cannot do without and compromise where you don't really mind!
OTOH, I find (you're the better judge, however) the tube pre a bit on the warm side, stronger in the mid (& upper mid) region So, maybe, speakers that are generally termed as very "flat", "a bit on the dry side", etc, could also apply.
BTW, SL make their own speakers; 1-2 models sound beautiful (but they are expensive)!