Power Cord for Synergistic Research MCC

Hi Mick
I auditioned every one of Synergistic's AC cords with an original MCC just as you have. My rig at that time was not nearly as revealing as it is presently, yet the test results were definitive even then. I now have an MCC-MkIII. Click on my username & then scroll down below my bio if you want to know the present rig's complete makeup.
Anyway, even with my older rig & the original MCC, the difference between AC cords was quite compelling. I didn't really want to believe that the AC cord would make any difference at all, even after discussing this with Mr. Ted Denney Pres. of Synergistic. Was I wrong!
I began the testing with a cheap stock AC cord, followed by the Master Coupler, the Reference AC, the Resolution Reference AC, the Designer Reference AC, finally the Designer Reference Squared AC. All of these cords were obviously pre X-series.
Every time that I installed a better AC cord, the depth & staging especially improved over the previous cord. This was the most noticable difference, although there's a greater sense of naturalness imparted with active shielded interconnects regardless of which AC cord was used. I ended up with the Designer Reference Squared AC cord & realized better bass definition & extension as well with that cord. Go figure; I still don't understand it, but then neither does Mr. Ted have a complete explanation.
Having recently upgarded to the MCC-Mk-III, now all 3 of my Designer Reference Squared AC cords are active shielded as well. The new X-series is all seriously even better.

Craig I have a Reference AC (pre X) just sitting here that might be of interest...you're welcome to try it.
The MKII unit went to the BNC connectors & better DC control cables.
The MKIII they upgraded the internal module(s) to X-series (this can also be done at home) & X-series DC control cables, remarkably resembling their Synergy speaker cable. Cheaper build cost & better HF & LF extension as well.
Anyone presently owning an MCC Mk-II might be interested in an additional module (2 are available) if you want to power additional active interconnects, speaker cables, or AC cords. Y'all know how to find me.

Mick I can't answer that question, sorry. The only way to know what will actually happen is to try it in your own rig. I can try to guess though...
It just might be a tie, so the best price might dictate the choice in that case. I am guessing an approximate tie because although the Reference AC was formerly a step up from Master Coupler, the Master Coupler you mention is upgraded to X series active shielding. Upgrade to X-series made a nice improvement on my DR2's, so assuming an equivelant enhancement (this assumption may or may not be correct) then the Master Coupler could be equivelant or perhaps even slightly better (or Not?).
This is all about synergy (how the individual parts react together as a whole) so as I said, the only way to really know for sure is to try it out for yourself. Even your personal listening preferences come into play here; the sound that I would prefer isn't necesarily the same as the sound that you would prefer.