Audio Quality Poor

I'm not sure what I'm doing wrong.  I've been working on music for several years, first with Producer 8.5.3 and now X2.  I think I know the ins and outs pretty good, but I can't figure this one out.  I've been working on voice overs for the past couple of years.  When you listen to the sound of a naked voice compared to music with a lot of tracks you can really hear if the sound quality is suffering.  The dense layers of music seem to cover it up.  Anyway, I'm recording the voice, exporting it as a variety of formats, Wav, and MP3 from 64 up to 256.  Playing it back on Windows Media Player or Sony Sound Forge there is a definite drop off in quailty.  A weird distortion is introduced.  I experimented with a variety of plug ins and having everything turned off, still bad.  If I record directly to Sound Forge, it sounds great.  If I play it back on X2 it sounds fine.  It's when its recorded in X2 and then played back on another software that it sounds bad.  Any help would be much appreciated!!!!
 

Are you changing bit depth from 24 to 16 without dithering?

The first thing you should always do to check your work is to re-import it into Sonar, solo it, and bypass any master buss Fx.
 
This should (WILL!) sound exactly the same as listening to the actual mix tracks, and you can safely eliminate Sonar as being the cause of any degradation.
 
If it doesn't, you've got a screw up with your routing somewhere (e.g. tracks going straight to interface, bypassing master buss)

If you are not exporting what you hear in Sonar, then it you are doing one or 2 of these things wrong.
You either have a routing problem and/or you are not setting up your export properties correctly. Its 99.9% always one of those 2 things or both of those things.
 
For routing:
1.)Tracks go to the Master bus.
2.) Sends on the tracks, if you have them, go to a bus.
3.) Buses go to the Master bus
4.) Master bus goes to Main outs 1/2 (sound card outs)
 
For Exporting properties:
1.)You basically should use 'Entire Mix' for your export source or 'Main Outs'
2.)If you want ot burn a CD or play it on the pc, you should set the bit depth to 16 and the sample rate to 44.1kHz
3.) If you are going down in bit depths, you should use a dither. POW1,2 or 3 are good to use. 
 
There you have it!!
CJ

CJaysMusic
If you are not exporting what you hear in Sonar, then it you are doing one or 2 of these things wrong.
You either have a routing problem and/or you are not setting up your export properties correctly. Its 99.9% always one of those 2 things or both of those things.
 
For routing:
1.)Tracks go to the Master bus.
2.) Sends on the tracks, if you have them, go to a bus.
3.) Buses go to the Master bus
4.) Master bus goes to Main outs 1/2 (sound card outs)
 
For Exporting properties:
1.)You basically should use 'Entire Mix' for your export source or 'Main Outs'
2.)If you want ot burn a CD or play it on the pc, you should set the bit depth to 16 and the sample rate to 44.1kHz
3.) If you are going down in bit depths, you should use a dither. POW1,2 or 3 are good to use. 
 
There you have it!!
CJ

One additional point of clarity on CJay's note above - if you chose "entire mix" as your export source, I believe that sums all outputs together into the export, so if you're using FX busses, it will make your mix sound differently than if you use "main outs" as your source.  I realize your issue above is more focused on the general audio quality of your exports and not busses sounding louder in the export than they should, but thought you should be aware as you work through your export issue, in case you notice differences in exports with different options.
Russ