I purchased the AS-P400 sub a couple of months ago to go with my Axiom M22's in a stereo system. I find the sub to be quite musical and, while I like to play my classical music at respectable levels, my wife likes rock/pop at ear shattering (to me) levels. The AS-P400 does well with both. I have not noted any chuffing and the bass still sounds tight and blends well with the M22's at wife-playing levels. Does BB not sell this sub or are they out-of-stock or just not displaying it? If you liked the 300, you might try to find the 400 as it may overcome you problems with the 300.
