Yes you can hook up another amp to it if the other one has a LINE/DIRECT OUT. Run the line out of "the other" to the AUX of your Crate. The Aux on the Crate acts like a LINE IN. It can be used to amplify "LINE SIGNALS" only. You would not want to hook it up to a "speaker out" or "EXTernal" speaker jack of another amp as these put out a powered signals to run a speaker. This would damage your crate amps input section tubes. : ok so what your saying is i can hook up another amp to it and all that good stuff?thanks Trevor : : : my 200 watt all tube crate stealth head has an AUX. IN input, wtf is that for, thanks, Trevor : : It can be used for a variety of things. Like a power amp for non-powered heads, such as the Gainiac/Gainiac2, Carvin Quad 4, etc. A rack or pedal multi effects unit may be input there, if it is post EQ, with no added couloring from the Crate amp. Or as a extra amp for a lesser wattage amp with a line or direct out. You could even run a CD or Cassette player through it to jam along with.