find quality mono recording(s) and hook up each channel to diff. cable. place speakers in same small area of room. use balance control and listen long enuf to make it meaningful. repeat, rinse. :) fwiw, i once accidentally turned my tubes A/B UL off and on quickly and the resulting surge and noise did not make me want to do that again! i'm no no electrical engineer obviously but the manufacturer did not issue that warning for no reason. as noted above a/b cable comps can be done in a more helpful way anyhoo.
