Recent Darlington purchaser here, although our vantage points are not even close!!!
Unlike you drewdawg- I had nothing tangible to go by for a comparison. I'm 65, and have my old vinyl from a teenager on, and lots of rock, jazz and classical re-issues. BUT- I never used a standalone phono preamp! I always made do with my receiver preamps, with my latest being the built in on my Yamaha RX-A1030 receiver.
I had the opportunity to hear some of my vinyl played back on another deck and preamp and it opened my ears and eyes so to speak. I did some research on preamps and noise, and read a lot about Darlington(right here in my home state). I thought about going to the MP-7, but figured if this thing was good I'd be extremely happy for the $300 so I bought the MM-6.
I just finished 30 days of power on with it- and played a few pieces here and there, and the first thing I noticed my my soundstage just completely opened up, and found that out while I was working at my desk, which is to the left of my left speaker! For the rest of the chain- I have a VPI Scout 1.1 and an Ortofon 2M Black. The 2M Black was starting to get on my nerves as it has a tendency to pick up a lot of noise.
So just tonight- I played my Classic pressing of Alan Parsons I Robot, and now playing a Speakers corner pressing of Les McAnn / Eddie Harris Swiss Movement, and am completely floored that sounds are now scattered and placed or arranged rather than two dimensional. The opening track I Robot blew me away with just how everything seemed to just roll out smoothly and it spaciousness.
I'm a very happy camper with the MM-6 and its such a huge change from what I had. Why I never thought of doing this before- I just don't know. Take a read at the massive FAQ over on the Darlington site. It goes in to a lot.
Chris