HI. I don't think the reason they sound tin cannish is due to your software. The key things to check in your case will be the basics, and the basic basics. Since you didn't mention anything about D/A conversion in your post, I have to assume that you are going in to your comp with an analog input. This is a big NONO, and it would be the first thing I would correct. The reason it's so bad to go into your computer from analog, is that your computer generates a massive amount of r.f. and e.m.i. (Radio frequency, and electro-magnetic interference.) This stuff will induce itself into the audio signal on it's way into the computer, adding undesirables to your track. If you obtain a D/A converter (in your case it would be a/d, but whos being picky..), and you get a sound card that allows for a digital input you'll be fine.

Other considerations are, gain(is your gain set properly? if the gain is set too low, it will sound tinny.), your room(has it been treated acoustically?), and finally does it really sound tinny, or are your speakers lying to you? Proper monitoring is very important.

You have to remeber that the quality of the audio will only be as good as the weakest link in the chain.

Good luck.