Ok, more info...

There's a Sourceforge project that has Linux drivers, but they're for the ISA and PCI cards (the ones that are supposed to already come with Linux drivers). So if people had to write their own Linux drivers for the ones that already supported Linux, I'm even less hopeful about the networked ones.

I just found the price for the 2 port Serial Hub Si: $635.
Or there's the Serial Hub ia2 which costs $679.

Both of those are way out of my price range for a 2-port term serv!