When tracking each instrument you want it to record as close to 0db as possible without clipping. Assuming you're doing this then each instrument will be recorded loud enough. So far so good. So the problem must be at mix down?
Make sure your Master fader (the red one) is on the 0db mark, that could be your problem. When mixing you want to make sure that the stereo mix is as close to 0db as possible too without clipping. if it occasionaly appears to go up above the 0db mark but sounds fine, then leave it, use your ears. If the mix is going above 0db and it sounds distorted (clipping) then slide the master fader down a little.
This will ensure that the master mixdown (I'm assuming you're using the internal mix down method?) is at a reasonable level.
If you are mixing down to an external source then the probelm might lay there, that's another story.
Note: You're unlikely in my experience to get the mixdown on your audio CD as loud as a commercial one. These commercial products have gone through the mastering process in order to boost the loudness - that's a skill in itself.
The other problem could be that you are not using compression, so you are most likely to get extreme peeks. With these high peaks you have to lower the volumes of the instruments to avoid clipping at hte peaks, therefore the overall volume goes down and you end up with a quiet mix in order to avoid clipping? Normalizing brings up the low parts of the mix closer to the level of the peaks making the whole thing sound louder (or reduces the peaks so that the overall level of all the music can be brought up to a louder level).
Hope that helps.
Incidently I took my 'album' all recorded on the Vf160 to a friend who knows about mastering, he said it was OK level overall but a little quiet and needs to be brought up a little - so there you go.
