I have a Rega Planar 6 with the Ania MC, using a Luxman Integrated (so it's somewhat similar in sound to your Yamaha.) It's a very nice match up and you are in the right ballpark. I had bookshelf KEF's and really enjoyed them, but I would say they were a bit bright. The trouble is, others will respond and say they aren't.
So to your question of what is meant by natural, warm, bright, you'll get a lot of answers, and I doubt you'll find someone with your exact setup to tell you what it will sound like. But overall, I'd say you'll be very happy either one. I would suggest however to avoid your own TT/Cart setup (Millercarbon, bless his heart, is a real hands-on guy) and just let the dealer set it up for you. That's one big reason I went with the Rega, it was all set up and ready to go for me. I'd rather listen to music then play with cartridge setup. Hope this helps.
So to your question of what is meant by natural, warm, bright, you'll get a lot of answers, and I doubt you'll find someone with your exact setup to tell you what it will sound like. But overall, I'd say you'll be very happy either one. I would suggest however to avoid your own TT/Cart setup (Millercarbon, bless his heart, is a real hands-on guy) and just let the dealer set it up for you. That's one big reason I went with the Rega, it was all set up and ready to go for me. I'd rather listen to music then play with cartridge setup. Hope this helps.