Is this the box for me???
I'm running a 70s Fender Twin. If I've read the radial website correctly, I can plug the speaker output of the twin into this box, then connect the speakers to the box, and not have to worry about blowing my amp up due to speaker load??
What kind of cable do I use to go from amp to the JDX?
Correct, the JDX runs inline between the speaker output on the amp and the speaker itself. Because it's a speaker-level signal going to and coming from the JDX, you need to use speaker cables. The JDX does NOT provide a speaker load though, so you cannot use it without a speaker attached (or a suitable load box in place of the speaker).