Once i get it to where i think it might be presentable, I put it in wav form. Burn it to cd, listen to it on my home stereo in different ways, that is different EQ settings and even flat (no eq) and i'll listen on a car cd player. To get it sounding as proffesional as you can you need a good editing program and just go to work trying different things.
As far as getting differents levels and such out of different instraments you'll need to upload each instrament on a separate track or put the music track from jamstudio on a track and use different effects or EQ. I've done it different ways depending on what i want out of a song.
I've sent some of my stuff out to some publishers and gotton some good feedback (and some bad)
but never had anyone say anything bad about the quality. I've been offered a few indie deals so i guess it's sounding pretty decent.I guess what i'm saying is i don't know anything on how to be a producer but if you have a good editing software (i use Mixcraft 5.0) that makes a big difference.
Hope this helps some. Let me know if i can help plus some of the others, Robert Hall in particular are way more knowledgable maybe he'll see your post or message him