This is the second time today I have linked to PJPros post on the RS1s http://community.whathifi.com/forums/t/325890.aspx . Just like you he feels that there is not much of a jump, in his case from the SR80s. Yet when I first auditioned headphones the SR60s were the first be ditched as I heard a good sized jump to the SR80s, more of everything.
You have a source and amp I can only aspire to. Even though you are happy with the SR60s, you have got to find a way to try other headphones and see if you hear an improvement. The AKG K701/2s and the Sennheiser HD650s spring to mind.