I am really grateful for all your help but confusion is setting in again! I'm sure I'll learn more in time but as of now terms like "subgroups out" are something of a mystery to me - I did say I was "technically challenged"!As I mainly use condenser mics and therefore need preamps with phantom power it looks as though the Fast Track might be better for me (maybe).
If it's any consolation, it took me several years to get to grips with PowerTracks and even now I only know enough to scratch the surface of what it is probably capable of. I first got it free with Band In A Box and actually gave it away because I had no idea what it was and later ended up having to buy it!