If you have this compensated line out on the back of the amp, could you plug this into a PC or soundcard for recording.

Surely it is already at line out level so would not be damaging, but what would you plug it into and how would you use it.

Any info would be appreciated greatly.
Yeah you can do that, you plud it straight into your computers mic in/soundcard in. Or if you have a USB mic, the USB port (duh). Just be careful on headroom when you hit the record button. Direct outs from tube amps have a tendency to be rather high in level so check all your levels before you start recording.