With the VSX-26 carrying some of the amplification duty, your best bet is to put the ICBM between the RP91 and the VSX-26. The other thing sometimes done with the ICBM (between pre-amp and amp) will only allow you to use the ICBM for bass management of your main speakers in your case.
Putting the ICBM between the Panny and the Pioneer will let you use the ICBM for DVD-A and CD (assuming the RP91 is your CD transport and you prefer the RP91's DAC to the Pioneer's DAC). It will not
let you use the ICBM for vinyl.
Let me toss out some ideas (discard if they don't really match your case very well) -- you're bi-amping your mains, which makes me suspect that they are pretty stout, possibly full-range or close to it. In that case, how critical is bass management for two-channel sources? (Many people prefer to let full-range mains work alone for stereo sources like CD and LP, which is part of why I ask.) From what I can tell about your setup, the source that most needs the bass management is DVD-Audio (which is what originally triggered the creation of the ICBM in the first place). And without getting some additional external amplification, I don't know of a way to use the ICBM as bass management for your entire system...
Hope that helped at all. If it only made your head hurt worse (a distinct possibility), I apologize.
EDIT: If your receiver includes some sort of "amplifier in" connections, which some higher-end receivers do, you might actually be able to connect the ICBM to the pre-amp outputs of the VSX-26 and then go to the outboard amps for the mains and the "amp in" connections on the VSX-26 for the center and surrounds. I don't know anything about your receiver, so I don't know if this sort of hook-up is possible...
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[This message has been edited by gonk (edited June 26, 2002).]