My thought would be to do just what you said -- not route the rear sub through the ICBM-1. The choice is made somewhat easier by the presence of only one LFE input on the ICBM-1. So if you have two subs that each get a separate input, as in your case, you can only connect one of the subs to the ICBM-1 (people with two subs that both use the same input are a different story, of course). It would also make the most sense to me to have the bass management for your speakers rely on the "main" sub (the front sub, your Velodyne) to handle the low-freq work for them.