Hmmm ... I have to admit that can't really remember what I did _exactly_ while mixing this piece, but I'm absolutely sure that I didn't try to "sweeten" the actual sound of the instruments too much; this is true for all "official" demos, BTW, as our aim with these pieces is to show the possibilities of the library as honest and "pure" as possible. (... opposed to the numerous contributions of classical or original music from users or team-members of the VSL on our Demo-site, where "anything goes", and everybody sticks to the old saying "If it sounds right it is right".)
Listening to the piece you mentioned again ("Bass trumpet and orchestra" by Herb Tucmandl ->
http://vsl.co.at/en-us/67/3959/4715.vsl# ) I would say that much of the beautiful deep low end comes from the soft Bass Drum-hits which add to the Pizzicati of the Double Basses. I seem to remember that the reverb was a mixture of convolution and synthetic reverb from the t.c.electronic System 6000, so this may give you a special feeling of depth, too.
Another thought: Most of the time, I don't _add_ energy in certain frequency ranges; instead, I _cut_ those few small resonances which tend to obscure the overall clarity of the sonic impression. Maybe this is what you like to hear - less "mud", so to say ... [:)] .... But as much I would like to, I can't give you detailed information on this, simply because I always decide from case to case what to do, and how to do it. I don't rely on a fixed set of rules or presets.
HTH,