this one is rated for 10 amps, if the subwoofer isnt extremely powerful you may be able to us it.

[Link: dealextreme.com]

you can teach it whatever code you want to turn it on and off.  i dont think it will do discreet on and off though. 


or for something  more high end that will do discreets and handle more power:

[Link: smarthome.com]


or you could go with an x10 system and use an i/r to x10 converter.  i've never tried this so dont ask me how it works :)