I could be wrong in my thoughts but I would have considered it to be like the stock AK100 - where the headphone impedance out of the external amp in the chain is the one that matters.
For mtthefirst's issue, I have to admit I've not experienced the 47 ohm headphone out issue but having said that, I never really used the stock Go-DAP X much (if at all) even when I had it for 2 months. Now that it's upgraded to the LME49860, I tend to use it a little more. I don't know if the headphone out impedance had changed 'cos I do know that VentureCraft could reduce it.
I'm kind of two minds at the moment :-
1) send the Go-DAP X back for them to change the headphone out impedance. Note that I don't call it "fix" 'cos they don't see it as an issue yet, so they will see this customising or tailoring to customer requirements.
-- or --
2) return it and get your money back as a slightly more agressive approach to make a point that the headphone out impedance does matter to the consumer.
About the DD Socket 1 though, I only heard the Muses01 but not the Muses02. From what I've read the Muses02 is supposed to provide better bass/treble extension however I want to hear it for myself.