I think i got a way to solve this issue. I worked with a projekt with about 20 tracks with real instruments, With good volume after export, here's what i did:
1. Make sure that your input signal isn't to high (I Use a firewire interface to plug in guitars, keyboar and vocals). You have to make sure that there's no distortion on input. Espesially with intruments with bass.
2. The track volymepanels to the left can't show any yellow or red, not even close, my loudest track was about 50%.
3. Before you export turn down your master volyme down to the right, alot. (around 20-40% maybe...)
4. export to disk, NOT to itunes. Desame song on itunes (withot any equalizers or extra volyme) sound distorted, but not if i send it to disc. I have no idé why........!
5.then send the same song back to GB, and do what this guy's doing: http://www.youtube.com/watch?v=BCHnXloH8_Y
turn up the peaklimiter as much as you want or intill it sounds bad and distorted.
6. I exported with the "project at full loudness" button ticked in both times and it worked for me. I also compressed to mp3 both times. the "project at full loudness" button has to be ticked in the second time when you use the peakLimiter anyway.
Be really certain of number 1 and 2. Still experimenting with this so let me know if it worked
Actually, yes. It's all about recording technique. First of all, never tick in the "export project at full loudness" button. Make sure there's no red/yellow on tracks. No distortion on input source. Make sure there's not to much bass frequencies on bass and drum track. This guy makes great tutorials in GB (http://www.youtube.com/watch?v=f-p3hYYWCas), watch and learn. I did.
when you export, export to disc not Itunes. Turn up the master volyme, for some reson it doesn't matter if it goes up to yellow/red here. I normaly have the master volyme maxed out. I can recommend you to get yourself a mastering plug-in. I have this one (T-tracks) it's great and it's free: http://www.ikmultimedia.com/products/trcs/
You'll just have to experiment with these things. It's kinda hard in the beginning but you'll learn. Then you can do fun and awsome things like this recording I made a time ago. http://www.youtube.com/watch?v=l3aOaJE_y7g
peace, good luck!
As i said never tick in the "export project at full loudness" button. If you export your project and it sounds bad, that means you did something wrong in GB. You just have to try it out untill you get in right. It's frustating in the beginning, i know..! Important that you have a decent headset for recording too. hope my answers helps!