Upgrade question/Advice - new sound card vs preamps

Currently I have a Lexicon Omega and was possibly looking at an upgrade. Since I have had the Omega for sevaral years and it still works fine as USB, I was wondering the following questions. I have no preamps and use the preamps in the lexicon. I do have a yamaha MG10 mixer. I am looking at ways to improve my sound and keeping the cost down to under $400 to $500 but the cheaper the better.

1) would getting a presonus firepod give me better preamp sound or should I just buy a preamp and plug into the lexicon.
2) would an Art TPS-II be better then the preamps in the Lexicon.
3) should I buy the preamp or buy the whole new firewire either the Presonus or the Focusrite Saffire LE or the edirol fa-66.
4) Would I see any difference in firewire. I mostly do acoustic guitar with 1 or 2 mics and use a Pod XT for electric.

Thanks
-Tom

www.soundclick.com/thomasmoore

I have a studio project c1 and a mxl 603...and for dynamic AKG 770. I mostly use the C1 and if i am using 2 mics its the c1 and 603.

-Tom

I have tried and it sounds ok and couldn't tell much of a difference.

-Tom