Not sure where this thread went but the simple answer is that IRIS is based on Cache and while it has extensions and enhancements you should still be able to run 'plain' Cache.  It's just a  bigger download.  I have run Cache and Ensemble both have been replaced by IRIS but everything is (or should be) backwards compatible.  The worst you would find is that you use a 'new' feature and should you even need to work on a legacy version you might find it does not work there.  The core learning should be perfectly compatible.