Interesting...I have the MZ2 and I borrowed a friend's GS-X MK2 for potential purchase a while ago. I had the HD800S at the time and not the SR1. Naturally this is subjective and possibly headphone-specific, but I ended up preferring the MZ2 in terms of tonality and imaging. Both pretty resolving. Don't get me wrong, the GSX II is an end game amp for many, but so is the MZ2 if your price range is <$2K (new MZ2 or used GSX II or new GS-X mini). With the SR1, who knows what the outcome would have been between GSX and MZ2. Maybe it is a better pairing with the GSX, but like many have mentioned in this thread, the MZ2 will be pretty good too. Where the GS-X Mini fits in relation to MZ2 or a used GS-X II is also interesting.
Ideally you can get to a meet or organize a mini-meet and hear all amps up for consideration to pair with the SR-1. For fun, I would like to try a handful of more affordable solid state amps with the SR-1....Gilmore Lite, Liquid Carbon, RNHP, Portaphile, etc. But, that's not a challenge that I would want to fund or write up
So many potential options for you.