B&W HT - searching for surround and amp

I have recently upgraded sound for my home theater. It is a large room (20'x30)') with 110 projection screen. Power is basic (Pioneer SC-27 receiver with 140 x 7 @ 8). Speakers are B&W Nautilus 804 front, 805 surround rear, HTM1 center, with a Velodyne powered sub (not up to snuff but ok for now since I am sneaking the upgrades in one piece at a time to fly below the radar) and a couple of Buttkicker LFEs with their own amp. Next steps are to finish speaker set and to enhance power. Two questions:

1. Speakers - what is a good surround speaker match for my 804, 805 and HTM1?
2. Power - I have been considering a pair of Rotel 1091 monos (500 watts @'8). Would the produce a noticeable improvement?