uh, to use that volume control you also would need one of these adaptors:
1/8" Stereo Jack to 1/4" Stereo Plug Headphone Adapter - RadioShack.com
and then if your headphones are only 1/4" plug, then you'd need also 1/4" female to 1/8" male adaptor as well .... Stereo Inline Adapter, 1/8" Jack...