[Wayne A. Pflughaupt]

are there any general "rules" how much decrease (in dB)/filter setting you can use?...or can you use whatever the "fbq2496" can adjust down..so to speak?...if you know what i mean..

Well, if you decrease everything across the board to where the 20 Hz area is, you’ll have to boost the volume back up to make up for the huge loss in sound level. That will have the same effect as if you had just boosted the below-20 Hz range. Might not be a good idea to try to boost up that low range by any method. However, if it’s a problem you sub will let you know – it’ll start making nasty noises.

Have you tried any other locations? Usually a good corner will get you the best extension.

Regards,
Wayne