Re: Cab question.
The headphone outs on most electronics, especially amps, are not direct line outs--they are compensated for lower levels. Whay you could do, and this will require just a basic knowledge of electronics/wiring, is to ad your own speaker output. To do this, take the two wire off of the Line Y speaker, splice in another two leads with a 1/4" phone jack female end. Then hook the original speaker leads back into the Line 6 speaker and you have the new plug dangling from the leads. Run a 1/4" instrument/speaker cable from that to your Marshall cab. Now you'll get sound from the Spider AND the Marshall.