I don't know much about mac software, so I'm going to keep my mouth shut! I still stand by my original assessment that a lower line G4 should run fine, however. The studio we recorded our trio record in has a G4 800Mhz machine running the newest Pro Tools (the HD) with all the plugins you can imagine and he has no problems.
For preamps, you can't go wrong with Grace. Of course, they are $$$$$.
I have a Presonus M80 that I like a lot, although I've read they've stopped using the Jensen transformers in them and went to a cheaper (and not as good sounding) alternative. Mine has the original Jensen's in it.
The True Systems Precision 8 is nice. Sounds real good. The Focusrite Red series is awesome.
All I know is that when it comes to preamps, you get what you pay for!