Okay, I can use GS to render PostScript.  I can send the output to a printer.
   Is there, somewhere out there, an existing script clever enough to just DWIM
   when output is sent to it?  If so, does anyone have a config file for an Epson
   Stylus Color 600?

Do you mean a print filter script?  Try magicfilter in pkgsrc/print.
You can customize it to recognize other file types pretty easily as
long as you know the magic numbers and have the appropriate conversion
filters.

I have used it for a Stylus Color 850 with fine results.  I would
think the 600 would be doable also, since ghostscript support for the
SC printers is reasonably flexible.

Let me know if you want more details.

Cheers,
Brook