Well, it sounds very good, but I have no idea what you're talking about. Can you describe what you're hearing using terms that describe sound rather than visual terms like "blacker" and emotional terms like "relaxed" or "busy"? Dynamics? FR? Distortion? Technically, the big difference should be dynamics, and if you can hear that, you would have to be compressing pretty hard or playing back at extraordinary volumes.
I totally agree with you about dithering. There is always one dither that works perfectly and a bunch that don't. You can't just blindly use any old dither.
At work, I used a ProTools work station that we used to record dialogue and music. We would always record and mix 24 bit to allow room for boosting levels. But once we finished the mix, the bump to 16 always sounded identical. If it doesn't for you, I'd suggest trying other dithers or see if there is something wrong with your software or hardware. It really should sound identical. My bet is your problem is in the transcoding. If you captured at 16/44.1 and avoided the bump down, it would probably sound fine.
As for vinyl transcription, going to 24 bit should only give added resolution a mile below the noise floor. It might help define transients for impulse noise reduction filters, but I always found that the minute (if any) improvement in noise reduction wasn't worth the crawl that my ProTools work station slowed down to. This was a few years back. Comps may have gotten faster and filters better designed for 24 bit.