PERFORMANCE REPORT - BI-AMPING RUMBLES:
I did it! I connected my J-Bass to the INPUT on a Rumble v3 200C, then an instrument cable from the EFFECTS SEND on the 200C to the EFFECTS RETURN on a Rumble v3 500C and it worked exactly as expected (pre-amp out to power amp in).
Then I reversed the connection: I connected my J-Bass to the INPUT on a Rumble v3 500C, then an instrument cable from the EFFECTS SEND on the 500C to the EFFECTS RETURN on a Rumble v3 200C. Again, it worked exactly like the block diagram suggests it would.
And it was glorious to behold, my brethren! 490W of Rumble bliss.
I had both amps with EQs all centered (noon), no overdrive, no tone buttons engaged, Horn Switch ON. Both MASTER knobs set to 9:00 (I got neighbors.) (Of course, the 2nd amp in the chain (the slave) does not use any of the tone or volume controls.) I very much liked the smooth, clean tone.
Sometime I'm going to have to fill out the rig with extension cabs for the full 700W insanity mode.