the little labs device would do the job, as will the radial
studio guitar interface, but if i understand correctly, with these devices, your amp will have to be next your cab, while you can be wherever...
what we are looking for is a device that will allow the cab to be 100' away from the amp/musician... essentially an amp to cab extender, as opposed to a guitar to amp extender. I have not seen such a device yet. Little Labs, Radial, Whirlwind.... anyone listening?
disclaimer: unlike dbubba, i do not know if running 30+ feet of speaker cable will degrade the sound, so i do not know if the need for such a device exists even...
respect,