JN,

thanks so much for the amazingly detailed response.

I can't match that post! But I will answer your initial question:

or one of my small room reverbs?

Yeah, that's what I do with great success. But don't overdo it. A little
electronic ambience goes a long way, and if you add too much it sounds
artificial. I often switch the bus Return on and off while the track plays,
so I can better hear how much effect I'm adding.

--Ethan