Because the 3 little bones in your ear (ossicles) are different in every human what you hear is unique to you and as such you must have an in-home test of both amps to get your ears happy.
That being said, (I'm biased) the ARC Ref 75SE is a fantastic amp that will play well with your Ref 2, It's a neutrally voiced amp that adds very little tonal expression to the signal you feed it. The amp has a wispy airy soundstage and has well controlled bass. It's faithful to the artists recording, and to my ears well recorded music sounds live and deep through ARC gear.
The Mc is altogether different. It's voiced to be warm and "Tubey" sounding which is great for some tracks but in my biased opinion is adding too much to the original signal. It's pretty, even sexy. It has good resale value. It just colors outside the lines too much for me and it's irritating to have a track that's supposed to be bright and sparkly sound blanketed.
I know this will tick off some people but the Mc is considered a "Mid Fi" product.