I am surprised myself, as I have not heard much other than good things (at least decent) about the Preamps of
the Fast Track Pro. I would look into other reasons for the poor sound quality, starting at the room you are recording in, the sound of the source you are recording, the mic, then the cable. Next, non updated drivers for the interface for your computer, or maybe a setting in your DAW. Worst case scenario, there could be a problem with your interface.
Before throwing $400 bucks at something, I would make sure you are not just missing something. I am not even sure your interface actually has true 'Line' input. The line in's may actually use the preamp stage, thus not giving you any benefit of an external preamp. And not to mention that it usually costs much more than $400 to achieve really useable results from another preamp (IMO). I have 3 ART preamps. TPS2, DPS2, and Dual MP. None of them are any better than my Tascam preamps. Just a bit different. I use them for scratch tracks, and enabling use of my 6 alternate inputs of my interface. I hardly ever use them because they add something. I have not however used the Voice Channel, though I don't think it is going to give you what you expect. Check the things above, then maybe you can rent, borrow, buy-return a preamp, and see if it gets you what you wish. I will bet $20 that it doesn't. Just sayin...
