Have a AV123 MFW-15 subwoofer, a giant 100 lbs. ported monster, in black. I bought it for my brother-in-law as a gift, but it's too big for them.

This subwoofer is notorious for bad amplifiers, and this one indeed has a bad amplifier. I have an amplifier which will work, an AudioControl Architect 200 unit that is 2 ohm stable, (so stable bridged to 4 ohms) AND has a variable 18db high-pass for subsonic roll-off... at 20 Hz. So would be PERFECT for this subwoofer. If someone wants more low-end bandwidth (the subwoofer was originally rated for 15 - 17 Hz. and has a port tuning of 18 Hz.) then other amplifiers can be used. Asking $217 for the subwoofer, or $263 for the subwoofer with the AudioControl amplifier which is 420 Watts RMS @ 4 ohms bridged mono. Dimensions are 23.94" x 18.125" x 22.44" H x W x D. Including an image of a fix for the amplifier that I found on the internet - but I'd feel better using it with a reliable amplifier.