I think Noubourne means the Sentinel
, not Conquest.
You have a very large space to fill, and it will be difficult for one <$700 subwoofer to do it justice. Fortunately you seem to find your BA PV500 to be adequate in terms of output, so you don't listen at super loud levels. Still, I have a feeling once you hear great bass you'll want more
As was previously mentioned, the MFW-15 is back up to $699 + shipping. That puts you closer to $850, well out of your price range. However, it would probably do a better job filling your large space than just about any other sub at that price. Hopefully some other MFW-15 owners will stop in, but my impression is that AV123 is finally getting the subwoofer situation under control. I still don't know that I'd buy a MFW-15 right now, but I certainly wouldn't
have just a couple of months ago. Another thing to consider is that AV123 has sales every 3 days or so (a slight exaggeration). If you're serious about the MFW-15, just wait until another sale pops up. It won't take that
At its current sale price of $649, the Sentinel is a good choice, though it'll still be a bit over your budget. I just checked and shipping to CA is about $85. I don't know where you live and shipping might be a bit cheaper, but you're still looking at a bit over $700. The Sentinel is a "safer" choice - no big amp fiascoes, etc - and is still a great performer, but your room is too much for a single Sentinel to handle (or the MFW-15 to handle, for that matter) if you plan to listen loud.
You might also want to look into the eD A5-350
. It has a big enclosure with a 15" driver and costs $800 shipped. The A5-350 likely has similar output capabilities to the MFW-15 and has a fairly consistent price (though it does go on sale from time to time). Support is also great at eD so that's something you might want to consider.
My recommendation would be to get one of these three subs. They're all great performers and should be a big upgrade over what you have now. Try one out and see how it handles the room. If you feel you need more output, get a second sub later. Your room really begs for at least two of these subs IMO, but given your budget constraints, I'd try one out and add a second in the future if you need it.