Hey surfer
I'm from Iceland too. Small world, ain't it ?
Well, i'm a poor student so I don't have much budget to buy gear. I understand exactly what you're experiencing because I've been using Pro Tools Le 7 (because I have an Intel mac) and M-Box for a while.
I just recently changed to MOTU's
Digital Performer 5 and I'm loving it. I get much cleaner and better sound than through Pro Tools.
Look, I understand why the mixdown you're listening to isn't as good as when you listen through the software in your computer. Answer = Monitors. That's what's wrong.
I'm kinda in the same position. I'm using very poor monitors. I'm just using my stereo, some old Pioneer amplifier and some speakers (very good for general listening to music). I manage to get decent sound because I know where the limits are. I know when the bass is too much and when the highs are too high. I just compare to other music I listen thurgh those speakers.
Now to get to the point. You need good monitors to hear every dynamic and every eq you've done to the mix. A common problem is that people tend to punch up the bass to much.
So I suggest listening through many types of speakers, monitors and headphones to balance everything. You don't always get great results at first. I suggest aftur you've exported and written to a CD, listen in different audio systems, cars and headphones to hear what's too low and what's cutting too much.
And by the way, Dithering isn't needed when recording 16 or 24 bit 41.000.. it's more used in high quality recordings such as 96.000 for DVD's and something like that. You won't hear much difference, if any