I tried it, and it didn't sound good, and got hum to boot. I tried it also with an impedance transformer; no better. Maybe someone here can explain why and/or a better way of doing it, but my attemps failed.
FWIW, I found a good-sounding speaker emulator box: my DC's speaker out goes into box; box has an out for the speaker and balanced out for a board/PA. Sounds great ...very little color change, and nothing I can't compensate for with a hair of EQing. Now I can control my amp's stage volume while the board gets a good, clean signal (and righteous tone, natch!) without having to worry about mic'ing or volume issues.
Edward