But this stuff can go even deeper than all that. Although some of it is simply frequency related, it's not just the constant presence of a frequency or harmonic layering, but a kind of motion that flows like waves through the harmonic layers. It provides spectral complexity that you can feel. Blahblublablah, it's hard to try describing it. I can't wait for my synth to be done, because it has a curious magic inside that even I can't explain. The not so magical part is the processing speed, but I'll try to work that out some more...
Another part of all this, though, is the modulation logic and performance powers. Even simple sounds can get damn near perfect brilliance, if the performance features for modulations allow for lively playing. This is not just for live performances, but even when you create patterns, it's the way it can respond to velocity and other modulations.
Oh man...way too much ground to cover on that topic, I'm afraid. Warmth, though, doesn't mean any specific frequency, that is silly. Warmth comes from gentle fluctuations and can be relevant at many frequencies even into the upper mids, I suppose. I can see, however, that someone would say 400Hz and lower, sure. And may I add: What the hell do I know?
...dang, I'm not a dsp-head or the likes (unfortunately). But I've been creating sounds and have dealt with digital music and synthesis for almost 30 years now. Hmm, yeah, that could lead to some trained ears, hmmm... 
(Hoping that that's a good thing, hahaha) 
