Run your Avalon to the modded A/D on your 003. Use this IO for your dry guitar tracks.
SPDIF back and forth to your Eleven Rack and set its Rig Input to the appropriate Digital Input (same for output). Grab the IO from the 003 SPDIF input for your Eleven Rig tracks. True Z should still be affecting your signal at this point.
Here is a link to a clocking article for this specific scenario since the BLA modded 003 should have a superior one that you would want to set as master.
http://avid.force.com/pkb/articles/e...ow_to/en345879
I haven't tried something like this but the latency between units should be minimal since no additional ADA conversion is taking place. Still a good idea to check for phase between your dry tracks and the Eleven Rig tracks.