Very nice account of your experience with ARC. Very similar to mine although I have spent the last few years with the Ref 160s and 160m.
Judging by your comments on your main system I must highly recommend the Woo WA5 headphone amp. If you can afford it add a pair of Takatsuki 300B tubes and you will be in the the same headphone nirvana which all ARC does to your main system,