From the manual: " Active instruments are those that have an internal preamp or a line-level output. Active instruments should be plugged into a D.I. box, which should then be connected to the mic input rather than directly to an instrument input." Whirlwind Imp 2 is a good direct box, if you can find one. Lots of other DI boxes out there too. I've used Klark Teknik and have no complaints. They have the reasonably priced DI10A. If you are wanting to capture the sound of the Spark amp, just throw a mic in front of the amp. You could get a DI box and a mic and record both channels for more creative flexibility.
