I actually use/have used Amplitube and I have had the same issue. The thing is that its an amp modeler--you won't get it to sound EXACTLY like a real amplifier and there is likely no way you will be able to get that chunk and oomph you are looking for. I spent many hours playing with the settings in that program and I was completely dissatisfied with the tone I was getting, then I just decided to find a way to record the guitars and it was a hundred times better. I think even a lower quality recorded signal will still be better than the amp modeled one, if you can manage to actually record the guitars. However, if it is just more convenient to use Amplitube, then you might just have to live with it. I even tried doubling the guitars, compressing it, whatever I could do, and I only saw minimal improvements but nothing that really impressed me. Maybe someone else has had a better experience with this? That's just my personal experience, so its something to consider I think.