Your room is slightly larger than mine. And yes, PL 300 would fill your room if it is untreated. I do not know the sonic signature of your Bryston setup. But these are quite easily driven. However, i do not see any negative aspects using a larger poweramp with them. Torque/ control - is always nice. When i mention that they adapt. I mean they change due to how you set them up, if you change anything in the system. They are not sharp/ harsh, on the contrary, they are quite smooth and as mentioned, very coherent. If you do as me, use draining of chassis, they become more prone to reveal even more of, placements, changes in cables and electronics. This is very nice, but it will require more causion. I could mention more of this if you'd like? (just mail me directly). If you have a room of concrete and glass, i would say acoustics/ damping is needed.
If you manage to control the environment (room treatment), you can set them up for nearfield without direct dowsides. The result is a fast sounding speaker, with excellent P.R.A.T. and impact. The sound is quite powerful and liveley, - no sleepers. The Bryston will help out. The ability of macrodynamics impact and still rendering microdynamics and the dynamical contrast is great. Further more, i think the placement is a thing you'll put time into. Because it is pending on how you'll like the soundfield.
Wide and large soundfield, or a more narrow with even better sense of holographic.
I would, i buying PL 300, start off with acoustics in your room. If this is ok to do for you? You will have a speaker that is a great all-arounder with very fast and detailed sound. You will probably, over time, learn the speaker and if you feel the tweaking is a bit of fun, it'll prove rewarding.
If you do not wish to address acoustics, they will be too large for that room and i would not recommend buying them.
If i take out my room treatment, they are simply put, overpowering this room.
As mentioned, you are always welcome to ask me, as of direct mail. I will tell you all that i have noticed.
I am quite picky, so i have tried and worked alot to make it become as good as i can get it:)