Rick, I took a look at the back of your 601:
And though they are not labeled as such, you DO have multichannel (pre) inputs, but they are only available for your DVD player. You probably already have your Sony plugged into them. And yes, the ICBM would go between your Sony and your Onkyo.
However, should you upgrade to a receiver with pre ins labeled as such, you still could only use the ICBM with one source. Receivers that have pre ins allow you to select which source uses them. Your 601 only allows the DVD to use them.
The ICBM has only one set of inputs and outputs. If you wanted to use the ICBM as a crossover for ALL sources, you would need to upgrade to separates, and install the ICBM between the preamp and the amp.
As for using the multichannel inputs for all movies, it would depend on whether the Onkyo or the Sony had superior DACs (digital to analog converters). If, in the receiver, you select the digital input coming from the Sony (see page 42 of your manual), then the Onkyo does the converting, and you are using the receiver's crossover. If you select the multichannel inputs in the Onkyo, then the Sony is doing the converting, and you'd be using the ICBM as your crossover. You would have to try both to see if you preferred one or the other.
Hope I haven't added to the confusion. I know I'M confused, and I wrote it.
