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I don't know if you're getting my messages....because they don't seem to be going through from my side...excuse me if I'm repeating myself.
On the Boston sub. Yes, I have one. Yes I think it's equal to the PSW505. Same general weight, wattage, 12" woofer. Dynamic peak of about 450 watts, 300 RMS. Cabinet inert and non-resonant. For 200 bucks you can't beat it. It compares to most good subs in the 500 dollar range. Also good with music if you back off the volume setting.
Was watching The Day the Earth Stood Still the other day with the sub a little over half volume, it was rattling the chandelier in the back of the room and the glass bookcase, and a bit of the floor. (Room 25 x 11.5 x 8.5) I'm happy with it for now.
Run it with M70s so it would definitely give you what you need with those 400s.
Hope this helps...