this is a tough call. I can't speak about the matrix 1s. Never heard them. The Matrix 805s are a good sounding speaker and were what I always to replace my old Infinity stand mounts with. The only challenge I see is that like all B&W speakers with the Kevlar Cones, they are a bit forward. Not my first choice with the Nova 150 as I would lean toward a warmer speaker. I agree that you might not like them.

Regarding the Kefs, Kef has a VERY LONG break in period and I am not sure whether my opinion of the Q line is justified as I find it forward/bright though reasonably detailed. Not my taste and potentially a tough pairing with the Nova, The LS50 I have heard comfortably broken in and it is neutral, highly detailed and wonderful for a small to medium room when paired with a subwoofer. I like them a lot assuming you are in the right sized room, have a subwoofer and don't turn it up to 11.

I would look seriously at the Wharfedale Jade 3s or the Reva-2s. They will have a warmer sound profile and IMO, will match better with the Nova.