what sort of adapter ?

You really want to run a line out (not headphones out as the impedance will be all messed up) of your amp to your sound card (sounds like you have the right hole but check the manual). If this is the case you probably only need either a balanced stereo 1'/4" female to 1/8" male adapter or a mono adaptor for unbalanced connection.

Laskies or Dixons should be able to sort you out.