Hi guys,
Newb here again, carrying on with striving for a great sound...
I've used a few compressors included with Sonar, like Sonitus, primarily for bass guitar tracks, and just don't find them doing what I expect or want.  I'm a guitar player, used to quality pedals, knowing what they do, how they sound, how they affect the overall sound.  For some reason I don't get that sort of result from, for example, Sonitus.  I can see the visual, the dot moving on the curve, up and down over the knee, and it looks ideal. But it doesn't really sound like it's compressing it properly. Mess with the ratio and threshold, but just don't get what I want.  I expect to be able to really smooth the bass track out, but seem to wind up pushing the plugin way too far without favorable results... it just gets ugly sounding.  For bass in particular, I'm not after subtle...  our player is very dynamic, and it doesn't come out well on the tracks.  Need it nicely compressed to make it smooth. 
Any ideas ?

Well, in that case I'd just fiddle in sequence until you get something you want.
 
For bass compression, first I'd dial in a good ratio, like 10:1 or some such.
 
Keep the attack fast (at first) and the release a little long. Start turning down your threshold until you're getting definite gain reduction, then bring the makeup gain back to get a level you like. If you miss the dynamics, you can slow the attack so some stuff pops through, even shorten the release. 
 
The Prochannel compressor is even easier because it's just one knob in and one knob out. 

+1 to wicked; the attack time will remove or allow the initial pluck of each string.
 
On a guitar pedal, typically not as many parameters can be tweaked as with a plugin (the missing ones are "built in" to the box), so understanding how each works and what it does is important. A good way to learn them is playing with extreme values at first (one at a time), then tone them down for a more musical application. Compressors are an effect that are beneficial to learn intimately to get the most from them (and used a lot).
 
Here are a couple quick articles I found worth reading, one specific to bass, and the other more general:
http://www.studybass.com/gear/bass-effects/bass-compressor-settings/
http://www.soundonsound.com/sos/sep09/articles/compressionmadeeasy.htm

Try the Sonitus Multiband, enable Limit on the Common page, and push the output a bit so it goes into limiting...not a lot. Then compress the other bands to taste. You'll need to bring down the track volume to compensate if you're pushing it hard.
 
If you want lots of compression without sounding like it's compressed, multiband works really well. If you have enough computer power, the LP-64 Multiband is cleaner, but it's more of a mastering compressor so it takes a lot of CPU.

BOOST11 is my gun....Believe it! (Everytime...)

Maybe this will help. 
 
Training Your Ears To Hear Compression In 10 Steps:

• Step 1 – Once again, grab your favorite mix and import it into your favorite DAW
• Step 2 – Insert a compressor and a phase flipping plug-in on this track (We will call this “track 1″)
• Step 3 – Duplicate that track. (We will call the duplicate “track 2″)
• Step 4 – Bypass the compressor and phase plug-in on track 1
• Step 5 – Use the phase plug-in to flip the phase of track 2 (now when you press play you shouldn’t hear anything. Both tracks are canceling each other out)
• Step 6 – Set the compressor on track 2 to limiter mode with the threshold all the way up (there should still be no sound coming through when the track is playing)
• Step 7 – Now gradually start adding compression to track 2 while listening. (You will now hear only the difference between the two tracks, therefore isolating what the compressor is actually doing)
• Step 8 – Continue lowering the threshold until you hear all the crazy distortion.
• Step 9 – Repeat this on individual tracks on your mix (i.e. the kick track, the snare, the electric guitars, the vocal)
• Step 10 – Write in your notebook what you are hearing as you increase the distortion. What frequencies are building up as you increase the compression? What are you missing from the mix? What sounds boosted? What sounds cut?

Again, the idea here is to experiment. With each element in a mix there is a slightly different reaction going on. With each compressor you will hear different tonal differences and distortion levels. The key is to identify what each of your favorite compressors is doing to a mix and to keep that in mind while mixing. So say you want a warm distorted compression, now you’ll know what compressor to reach for.

mettelus
 
 
Here are a couple quick articles I found worth reading, one specific to bass, and the other more general:
http://www.studybass.com/gear/bass-effects/bass-compressor-settings/
http://www.soundonsound.com/sos/sep09/articles/compressionmadeeasy.htm

excellent reference  !!!

The prochannel has some bass presets. I am not a guitar player but I thought it sounded quite decent on my vst bass.

Another thing to consider is that an effect is totally clueless about the signal it sees (it is dependent on the user to feed it properly), so relying solely on the compressor to do the grunt work can cause issues.
 
Without seeing your specific situation, a few things I would do for that signal before it sees a compressor:

1. Normalize it (to -0.1dB) to bring up the peaks (this will also bring up noise).
2. Gate that signal to remove the noise you brought up (possibly into the audible range).
3. HP/LP that signal so that only the context important to the bass is passed to the compressor (bring in each filter into the meat of the signal till you can hear its effect, then back it off a smidge).
4. Fiddle with recommendations above for the compressor itself.

Your situation seems more like a limiter function (high ratio desired), so realize that with a high dynamic range on the signal that you need to be sure that noise is not fed to the compressor, or the compressor will be more than happy to gain that for you too.

The main thing to remember is compressors that are designed to work on a channel insert or buss is a completely different animal from a stomp box designed for guitars! A good bit of studying the articles above and some others will get you up to speed pretty quick with a little experimenting on some tracks in your DAW.