This is something im on a mission to suss out too mate, from what ive learned upto now its about filling out frequencies, reverb can play a big part in space and warmth but as you say EQ is one of the main tools.

I have gotten good results from widening certain sounds, strings for example seem to sound a lot fuller when widened into the mix, waves stereo imager is good for this but im sur etheres loads of other plug ins that do the same.

a tight reverb on certain things i find helps smooth them into the mix but spread them out also.

Getting a good bottom end to your sound can help define it, i have been using waves maxxbass plug in recently for this, i dont know how orthodox my method of using it is though, i have been importing the final .wav master into soundforge then highlighting the whole thing then copying it for later, then i apply maxxbass plug in to the whole file within soundforge leaving me with a processed file consisting of a deep bottom end, ithen (paste special/mix) the previous file over the top leaving a deep bottom end but not altering any of the other frequencies, works a treat as far as i can tell :)

to be honest i expect you probobly know more than me on this mate lol

im listening to a cd at the moment through my monitors and it sounds light years ahead of what ive managed to do with my own music, a lot of practise is order