I would consider 91dB to be solidly in the "middle" sensitivity range.
30 sq m is not that big, unless you have a high ceiling.
You say you listen at low volumes, so I take that to be maybe 70 dB (typical conversation is around 60 dB, alarm clock around 80 dB, lawnmower 90dB).
If you get something with 250W, that is roughly 2^8 which equates to 24dB of gain compared to 1W, so now you're sitting around 115 dB.
This isn't to say you *don't* need 250W, and you have to account for dynamic peaks (usually 20dB or so) above your median listening level... but I'm just saying maybe it isn't as much of a necessity as some people say it is.
That said, I also really enjoy the SPL Performer line of amps (I have the s800, but they have several other stereo and monoblock versions).
