You will also need to control the room resonances. If you try for row ten volumes with full orchestral SPL the room modes will overwehlm your listening experience. While the previous posters are right that it would take more info to be completely accurate, a rough guess is that with speakers of about a sensitivity of 92 db, with room treatment, a 150 watt amp would suffice and still have enough head room to prevent clipping on peaks. On the best orchestral CD's peaks can be 10-15 db above average spl. orchestra
