The DJ mixers won't manage a balanced send. But that led me to the answer - if I can find room in the hifi cabinet for it - my larger DI box - use two channels, phono to jack from pre-out on the Pioneer into where the guitar would plug in, jack to phono from the "through" on the DI box back to the main in on the Pioneer, and long mic leads round the room to the mixer amp. Voila! Must try it soon.