Are you using softsynths? If so, make sure your audio and midi volume levels are up on each synth.
That one has gotten me a couple of times...

Otherwise, for me, it always seems to be the mix and main out levels as stated above - watch your meters..

V

When I export a mix down to a stereo file I always route everything and I mean everything through my master buss and select only it for the export. I do not select all the tracks or "what you hear" ever! Just the master buss. I have been doing it this way for a long time and can report no problems with doing it this way. 

There was a bug in Pan Law implementation that was finally fixed in X1 I believe.
Check what yours are set at. Do some experimenting with different.types.

It's been 9 months. I wonder whatever happened to Rick. Did he discover a "duh" fix and was embarrassed to say what the resolution was? (Rick, we've all done that!) Did he just not like the advice given? (Hey, we're unpaid volunteers, man. You get what you pay for.) Did he give up and move to Reaper? (They're a helpful bunch over on that forum, too, even if the SNR is about the same as here.) Did he bag the whole thing and go back to mastering full time?

I am having the same issue.  Using just a softsynth drum track and audio bass track, playing direct from Sonar X3, the master volume floats between -3 to -6 db.   When I export these tracks and reimport into an audio track and play that track the volume floats between -18 and -12 db.   Trying to find a solution.  PS all faders are on 0.

You should really start a new thread.. This is a year old and people will waist time reading the old posts until it dawns on them the year is wrong...like me... 

John
When I export a mix down to a stereo file I always route everything and I mean everything through my master buss and select only it for the export. I do not select all the tracks or "what you hear" ever! Just the master buss. I have been doing it this way for a long time and can report no problems with doing it this way. 

I realize I'm responding to an old response to and even older (twice re-awakened) thread, but I second this approach. This automatically excludes sends to headphone outputs or other external gear, and guarantees you get what you hear if Master bus is the only thing going to Main Out and Main Out hardware bus level is 0dB (something for the most recent poster to double-check).
 
I also often take the intermediate step of bouncing the Master bus to a track that outputs to Main Outs. This gives me an archive of the finished track that's tied to the project and allows for real-time A/B listening or null testing (with phase inverted) against the live mix on the Master bus. If that checks out, I export the bounced track with Source=Tracks.

Cactus Music
You should really start a new thread.. This is a year old and people will waist time reading the old posts until it dawns on them the year is wrong...like me... 

He already has... I just realized this is the same poster:
 
http://forum.cakewalk.com/Exported-Mix-sounds-terrible-m2988961.aspx
 
I suggest we keep the discussion over there.
 
 

Hi Guys, I'm not a specialist but I had the same problem and I might have found some kind of solution. 
The issue here is not that Sonar renders at a lower lever but it playbacks about 6 db  higher than media players. 
So If you want a more realistic playback you might lower your master level at -6 db and get it back on zero before rendering or if as me you have done your mixing already then move your master all the way up to 6 db and the rendering will be at standard volume.
 
I found this because after I render my mix inside Sonar And found it ok, then I looked for the audio file and actuality sounded lower outside sonar, so the the problem could not be the file but that Sonar playbacks louder.
 
I have heard recommendations about mixing at a lower volume or importing your reference tracks. This might be one of the reasons why. 

Oh, no, it's... The Thread That Woudn't Die. 
 
Meter levels in SONAR are based on digital signal amplitudes. If the hardware out bus shows peaking to 0 dBFS, that's what's being sent to the D/A converter of your audio interface, and that's what will be exported if you use that output as the Source. If some other player sounds quieter playing the file exported from that output back through the same interface and/or shows a lower meter level, then either the player is doing something to the level being read from the file, or something was fouled up with the routing or export selections such that the source you exported was not the source you were monitoring.
 
It's really that simple. It's just hard to figure out what the issue is in a given situation, remotely, without being able to see every project and hardware setting firsthand, which is why these threads tend to do on and on.