Bucking magnets are great for putting speakers next to monitors- but I don't know if you can count of perfect cancellation of magnetic fields in all directions. Which might be important if you're going to have your hard drive nearby.
A little magnetism near a monitor = you need to degauss.
A little magnetism near a hard drive = you've lost your hard drive!!
Maybe you should put an audio line-out on your controller next to the video out, and use the tv speakers, or home stereo. Or a headphone jack. Or build your Xplods into separate enclosures, that you could plug into your controller, but set far away.
Or, try it out anyway, it might work fine!

I offer warnings and alternatives, but don't insist that I'm right.