I know what it's like to have to give up a solid interface for something new and unknown, it's never easy.
But you mention external mic preamps. Well, I'll tell you that if they're high-end pres, you are not getting your money's worth. Sending that transparent or big and warm signal into the converters of those ancient sound cards is, frankly, self-defeating.
There was a thread here recently where someone remarked that going from an old interface (Layla or Delta, I don't remember) to a new one, he noticed a striking difference in the quality of sound -- just a lot cleaner.
I could only concur.... I and a number of friends noticed the same thing when we got rid of our ancient Delta 1010s for something new. Though we went in different directions with our new interfaces, everyone still used the words "night and day" difference. It all came down to the newer, better converters.
So my recommendation is to start researching for a new interface, and maybe sell those old cards for what you can on Ebay.
Something to think about....