I wouldn't downsize at all. If it were me I'd want 2 to 4 of them things in your enormous room... There is never such thing as too much sub, if its too much bass just turn the sub down. Using a smaller less powerful sub you would probably be running near its max which is much harder on the amp and driver, so by using a big powerful sub at only 1/4 power you will extend the life of your sub by a long time. Another thing you could do is invest in a Radio Shack Digital Sound Pressure Level Meter for about $50. Then before you run Audyssey set the sub trim in the AVR to 0db, then adjust the gain on the sub's amp to read 75db on the SPL Meter at the main listening position (MLP). Then run Audyssey. Then use the digital SPL meter and set all channels to 75db (which for sub will be 0db trim level in AVR), which is calibrated for Reference Level. Then from there you can adjust the trim levels lets say in your center channel to have louder voices and then you can keep your sub trim level in the AVR at 0db or you can adjust it to -6db, -3db, +3db or +6db or whatever db to get the desired amount of bass. FWIW I run everything at 75db, BUT the Center at +6db hot or 81db and the Subs at +6db hot or 81db.