Im not familiar with the Mac and AR preamps you mentioned above. I would seek out a online McIntosh community of owners and get their opinion on the c1100 and same for the Audio Research of community owners on their take for the ref 6se. I’ve collected stuff throughout the yrs. I have a few of extremely well regarded preamps because I chose to pick up a few of the best picks from audiophile friends that they’ve heard. Each one of my pre’s has its own unique character, but a thing that I have noticed that separates a reference preamp from a very good pre is the size of the presentation. A truly reference preamp is gonna be EXTREMELY open to the point where one cannot detect its boundaries and it will throws a gigantic soundstage with great dynamics. So as you’re evaluating preamps, I would take note of its openness. It should sound like there are no walls or boundaries to the presentation. This should not only be evaluated with loud playing or certain tracks, but most importantly the music should have absolutely no boundaries even at low level and this should be evident on all the different types music played.