You are correct about the ICBM's rear surround being a mono channel. We haven't heard anything about a new ICBM, but that doesn't mean we won't see one. In the interim, one solution would be to set the rear surrounds to small at the processor (since any processor with PLIIx would also easily allow this) and let the bass from them go to the mains or the sub, then just bypass the ICBM entirely with those two channels.