I realize this isn't Mini specific but I have this amp that I took out of my old mini when I upgraded my sound system. I did actually have this working with an HK enabler as well as aftermarket front door speakers because I had the Harman Kardon system in the old mini. I used this amp when my Harman Kardon amp had died and it worked awesome! it powered 2 12" subs.

http://www.crutchfield.com/S-rQnWFW3...fo#details-tab

There is a link with all the specs on the amp. It is no longer in production but this has been my old faithful amp.

Not sure on the price but if anyone is interested shout out a number and we will see if we can make something work. Thanks!