I am a newbie when it comes to tube equipment. I have had the ARC Ref 3, Ref 110, and Ref CD7 for a couple of years and they are my first set of tube components. Has anyone experimented with tube rolling with any of these units and what are some of the favorite flavors of either the 6550 output tubes in the Ref 110 or the 6H30s found in the Ref 3 and CD7 relative to the stock tubes that come from Audio research? Also, are there any issues one ought to look out for if one were to experiment with tube rolling with these components? Would appreciate any input Jonathan Valin might have on this given his familiarity with the Reference line from ARC. Thanks very much for your help.