Hatstand... I think that may actually have helped... it's definitely louder... I will test it in other pc's but seems to make a difference... so is it taking just the master track for it? what do you think about the other options you get for the mp3? (enable pass filters and such?).. i'll research more on it.. thanks again everyone.. seems to get better...

To me anyway,  this has always been common when going from my nearfeild monitors to my PC speakers.
Different speakers is usually the culprit. that's why the suggestions to import to Sonar.
-6db when it peaks is around ball park for Mixdown. -3 to -6db is what your looking for before master.
I would use this copy as your finished mix. Import it back in to Sonar on a new project and master it.
What you have essentially done by mixing it at -6 is save some of the of the dynamics of the material.
This is exactly what a mastering engineer wants to see when he receives your finished mix.
 
As I said, import this version in to a brand new project and create yourself a mastering FX chain. (See mine below)
A lot of good reads here on what your levels should look like when mastering.
http://forum.cakewalk.com/Your-Mastering-Level-m3524365.aspx
Here's mine:
My Mastering Chain consists of:
1-Linear EQ to drop off/filter APPROX 30HZ and under.
2- the SSL Bus compressor
3- CA-2A for Analog coloring= a 1 to 1.5 db push / very subtle.
4- Then the L3.
5- Followed by the L2.
6- Some  more light Analog coloring.
7-The Secret sauce.

should also calibrate the monitoring levels  - use a -20db pink noise (you can find some nice WAV files) and a loudness meter to set your SONAR outputs to match the -20db and your monitors to 77db or so. cross check all monitors. then when mixing turn it down (preferably via a single knob controller or in the master bus) so it's really comfortable to work with. you'll then find that you tend to push up the overall level on the master output. final levels should be set as part of a "mastering step" whether it's integrated in the master bus or via another bit of software. A/B your mix with one or more pro recordings to get your levels in the ballpark (e.g. if the track you're referencing is -18 LUFS, then make adjustments to yours to get -18 LUFS)

I always use "select none" I forget why, but I think it has just always worked where as Select all doesn't always work.
 
But one issue I see is your exporting to MP3 without trying exporting to WAVE first. 
To check your signal path always mute the master buss. All should go silent. 
Export to a WAVE 16 bit and try playing that. All your masters should be WAVE, MP3 trashes things and is only needed to post on line. 
 
Download a free wave editor like Wavosaur or Gold Wave to check your Wave file
http://www.wavosaur.com/
http://www.goldwave.ca/
 
Gold wave has a real good MP3 encoder which can also batch process a whole album. That's how I convert. 
But playing a wave file in a wave editor will give you tools to master  your song and check the levels. 
For $99 you can buy Wave LAb which has the all important  Average RMS level analyzer which is what you need to make sure your song is the porper level.. Peak levels mean nothing. One little peak can  make the rest of your song too quiet. Average RMS level is what tells us the real truth. 
 
 

Cactus Music
I always use "select none" I forget why, but I think it has just always worked where as Select all doesn't always work.
 
But one issue I see is your exporting to MP3 without trying exporting to WAVE first. 
To check your signal path always mute the master buss. All should go silent. 
Export to a WAVE 16 bit and try playing that. All your masters should be WAVE, MP3 trashes things and is only needed to post on line. 
 
Download a free wave editor like Wavosaur or Gold Wave to check your Wave file
http://www.wavosaur.com/
http://www.goldwave.ca/
 
Gold wave has a real good MP3 encoder which can also batch process a whole album. That's how I convert. 
But playing a wave file in a wave editor will give you tools to master  your song and check the levels. 
For $99 you can buy Wave LAb which has the all important  Average RMS level analyzer which is what you need to make sure your song is the porper level.. Peak levels mean nothing. One little peak can  make the rest of your song too quiet. Average RMS level is what tells us the real truth. 
 
 

^^^^ Listen to Johnny. I agree with every point he makes and follow the exact same routines when mixing/mastering