If you want a better bass shaker for less, just pick up a cheap subamp, 12" driver, invert it in a 16" round x 24" high sonotube vented into the end of a sheet of MDF supported by 2x2s under your couch. Makes a platform about 2" thick and the whole thing shakes, therefore your couch does too.. (and your feet) The sonotube also makes an end table..

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=300-796

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-185

Does the job of 3 or 4 shakers...

Could do the same with an LFM1 I suppose...