Karyn has a lot of great advice on details already, but I will throw out a mixing "big picture" to consider. A song is akin to a book, so each section (chapter) needs its primary focus on what is most important. The listener needs to feel logical shifts in this focus. Volume reduction and pauses leave "residual perception" of preceding material, so what comes next into focus (like vocals, instrument phrases, etc.) can take center stage. There are many ways to facilitate this, but keep the logical shift in focus for the listener in mind when mixing.

As you are mixing in SONAR, consider volume automation (or even pauses) to loud sections needing to "relinquish focus."

Could you expand a little more on what you mean, mettelus? You're referring to contrast?

Yes, but also what the listener is hearing (and what they remember). Example, many songs start with a repetitive, catchy riff, which is repeated throughout a song. Once a listener has heard it a few times, they will remember it, so the volume no longer needs to be "loud" to be heard (and can also distract from what you want to be heard, especially vocals). When mixing, moving the listeners focus logically is important, and things they have heard repeatedly become "ingrained" so even at lower volumes (or paused) the introduction of new material can occur seemlessly. Volume changes can be very subtle, but incredibly effective (i.e. -3dB is pretty substantial, but leaves "room" to be heard... plus "frequency masking" is a phenomenon where the loudest of things at the same frequency will "be heard").
 
Listen to something similar that you like and hear how they do it. Separation of material is most often done with panning/EQ/volume (the settings on a console strip), but volume alone can be incredibly effective (bear in mind that reverb is the "perception" of being far away, so be wary of using reverb on something which should have focus).
 
For some reason, as I typed this "Bad to the Bone" came to mind... very loud intro of a repetitive riff, then drum/another riff... when the singing starts, that riff is only done at the end of each line, and on a sax which is much quieter, but the audience "gets it." During the sax solo, the guitar volume is reduced dramatically, but still there and audible, but the sax has focus.
 
As Karyn mentioned, brass can get LOUD, so be conscious of the frequencies they are filling and if they need to be "that loud" to be effective.

Ooh, I understand the phenomenon you're talking about. I actually incorporated some of that technique for the piano, though there isn't a lot of repetition in this arrangement at all. 
It's "Let It Snow"- but there are some small break in there. It's in the Songs area if you guys want to take a listen!
 
 
 
Edit to correct link,   Karyn

Mettelus,  the main aim here is to produce a recording to use as a backing track so it sounds as if the band were actually there.  All the tips and techniques I've been offering are only relevant to a live sound situation.
 
I agree with you about the use of dynamics to focus the listeners attention, but that is more of a studio production and arrangement technique,  we're trying to fake a live performance..

Add an organ part if you want to. I understand what you are doing, more additional things in the song section of the forum for you to ponder about.
Nobody said it would easy to do though. And the rest is up to you.
(and it may be somewhat easy depending.............).
I would just have an idea of the sound stage and how it should sound to me and how it really appears when listening to it on the speakers. I sure you can imagine that.
 
It don't mean a thing, if it don't have that swing.
http://www.youtube.com/watch?v=qDQpZT3GhDg