Everybody I know who has gone back to vinyl has eventually gone back to tubes. I would get rid of the McCormack stuff and get a good tube integrated. Just my opinion
You seem convinced your preamp is the problem. But it could
be the speakers, either the design or the placement. I
remember when I had my Harbeths, I had to send my amp for a
repair and I was using some cheap Onkyo receiver I bought on
Amazon for like $180 and it sounded damn acceptable. IMO, if
the speakers work well in the room, you'll like your system
better. The best Steinway in a hall with crap acoustics
sounds like crap.
OK then I will tell you to beware the Conrad Johnson, the ones I have heard are very warm almost hot. The tuubes they use are 12AX7s and an occasional 5751. I love 5751s myself so it would a toss up for me. However you like the McCormack SS, for ? reason? vs. tubes. If you are willing to buy tube gear then I would unequivocally give you one more preamp to take seriously the AES (Cary audio. You can get this brand at Upscale audio. Simple and relatively inexpensive. He sells many brands to consider, but I Would include tubed power amps, that's My opinion. The AE-3 a true voltage multiplier and is very good compared
If you believe that your pre amp is causing the grain and thinness you described, I would concentrate on finding some demo pre-amps to try in home before purchasing. You're at the point where in-home demonstrations for costly items is important. People here and other places can and will recommend equipment for you, but, their taste and ears aren't yours and when you take their well intentioned advice and purchase site unseen or in this case ear unheard, your open yourself for major issues.
make a short list of pre-amps in your price range, find dealers that will let you take it home for a week or so and listen.
If you can't take it home, then go to them and really listen carefully. But, don't buy before you hear it on your stuff or equipment very similar to yours.
Also, just me, but I wouldn't limit myself to new because of warranty issues. For the price of a new pre-amp, one can purchase a previous top-of-the-line pre-amp for substantially less than the lesser quality "new" pre-amp.
If it works, it works. Ask substantive questions regarding the product. Tube life, etc.
When I sell equipment I like it when the potential buyer comes to my home (I know) and listens to the equipment with their music. That way, they see the quality and know it works.
Anyway, look around first.