There are a lot of other aspects that also go into the "sound" you are seeking.
Fat, warm, analog can be interpreted many ways. What Mics, Pre amps, monitors, are you using, how your room sounds, gain staging the pre-amp input/output into the focusrite .....ect....you get my drift....
basically there is no magic bullet in my experience, its a game of "inches" with
very few upgrades that will seem like a "foot"
Its kind of like cooking, 15-20 different ingredients all come together to make a
meal. If you miss a few ingredients the food will not taste right...
Same with the Production of a song, start with a good song, played by good
musicians, recorded in a good room, with proper mic's and decent preamps & converters, mixed on good (or close) speakers should sound pretty good once
it reaches the mastering stage. Your music will "taste" right.
Every once in awhile you make an upgrade that you can hear right away and
that becomes your new standard. For me, that was when We switched from a
budget ($400) interface to a mid-range $800-$1000 interface. And it was an audible/noticeable improvement. That was a "foot" upgrade for me. I also couldn't hear the difference before the monitor system was upgraded...
hope this helps...