FYI, you can record with the Eleven Rack using all of the inputs. You could be using the guitar input, the mic input, the two channels of digital inputs, and the two line inputs all at the same time in Protools, each to their own tracks.
So if you can get some kind of splitter, then you can have one cable going to the 11R's guitar input, and the other to your amp, and the mic for your amp can go into the 11R's mic input.
Here are a few to look at, and several of them have a mode to use both outputs at the same time, which is what you want (the Switchbone at the bottom looks very interesting):
http://www.sweetwater.com/store/sear...=aby&Go=Search
If you want to go high end, the Radial JD7 ($1099) is the king for this type of thing, but you're paying for a lot of features and outputs you may not use.