Well, you had the 520 with a much never version of ARC.
The MRX300 came with an older version, that was not quite as straight forward. I was allways a bit sad that ARC wasn't upgraded on the MRX300.
I find the latest versions of Dirac fine to work with (note that Dirac got a major overhaul about a year ago), and the sound quality is very good.
Whether its as good as ARC genesis, thats another question altogether, that I cant answer.
I think both are valid choices.
If Savage ran ARC with his phone that seems to me to be a distinct convenience advantage over Dirac, which still (if I'm not mistaken, which frequently I am) requires a laptop or nearby desktop computer.