upgrading from McCormack DNA-1 to.....?

I doubt it's the McCormacks. Have you tried the SL3s in your room with another amp?

I agree with Kr4, it is not the amp. I would look at cables, the preamp or speaker setup first. The Mccormack does an excellent job with ML's.

Tube preamps sound great....on paper. They seem logical to many, while newbie audiophiles fall all over themselves to get approval of their peers by having tubes somewhere in their setup--wouldn't be an audiophile without tubes, you'll hear and then feel. Sad truth is that, dollar for dollar, tube pres more often then not just don't sound good mated to a SS amp, especially if the owner values the strengths of their silicone amp. At your price points, if you like the speed, drive, "impact" and the specific warmth of SS (or your maggies, more likely here I'm guessing), you're not going to like tubes. Again, for the money you have to spend, if you value bass at all, you're not going to like tubes, they can't get it right, IMNSHO. Once again, without the bank roll of Bill Gates, if you like a crystal clear and extended topend, you're not going to like tubes either. Before someone beats me to the punch, a piece of free advice, "there are no magic tubes" just as "there are no magic cables" and "there are no magic isolation devices;" no amount of polishing can make a turd shine. Don't let folks talk you into spending a fortune on tubes or cabling.

Another thing, much of your gripes apply to ML's as well, as they are not that good of a speaker for your ideal of "impact, drive or warmth" as I find them one of the worst bass handling speakers ever, definatly not warm in nature. You probably should have stuck to maggies and added a powered sub. Maggies don't look as cool but they sure do impress where it counts, with their sound.

Just some different perspectives then what you're likely going to hear....

Well, if you want the perspective of a previous McCormack amp owner, I'd say a tube preamp is mandatory, especially an Audible Illusions preamp. I've never heard the Y-S preamp, so can't comment on how that'd mate with McCormack.

Also, the McCormack can be further upgraded by the designer himself to sound even better (stock McCormack's are a tad bright and not so refined for my taste).

I would suggest you try the bigger Maggies, 1.6 or 3.6. The DNA-1 dlx is a great match with both Logans and Magnepans but I find the Maggies´ (3.6/R) voicing warmer and smoother sounding while the ´stat panel of the Logans (SL-3 and reQuest) had the edge in clarity and detail. Didn´t like the bass though.

Just recently going from a B&K 200.2 to a DNA-1 Ultra Platinum, I can say without a doubt, it was not a step backward....but a jump forward.

I don't believe you can point the finger at the amp when you change the preamp and speakers at the same time. I would speculate the Maggie's just sound better, at least to my ears they do with the few that I've heard.

The McCormack will let you hear what changes you have made, by a wider margin than the B&K, not putting down the B&K, it's a fine amp....but the McCormack is safely a step above.