Interesting suggestions on here...many I personally don't view as 'warm/round' but more on the fast and articulate side of things (which is far from bad, but if you say you want a Brunette a Blonde isn't going to do it). Warm and round to me means audible harmonic distortion and either an attenuated high end or bump in the low mids with maybe a slightly limited bandwidth and some phase shift. In other words obvious coloration and lots of it. Something in the Neve(ish) or Telefunken camp (and their respective recreations) would qualify for this (but not so much anything API-ish), the Chandler TG or Germanium, or the more colored tube preamps like Manley, Tube Tech, or Mercury (which are very similar to the Telefunken preamps). Just my two cents of experience.