DocuSP Servers are available from several sources, they appear on EBAY frequently. If you are planning on running Solaris 10 you will need Blades or X86 boxes.
There is no "freeware" alternative as the software would have to talk to the onboard IOT firmware, and I doubt that Xerox would license this code. Re-inventing that wheel would be a monumental task, the the market would be very small. If you're on Xerox service, the software and licensing is included in your FSMA Xerox spent about 10 years getting DocuSP "right" -although from the beginning it was a big improvement over the DT135. The size of the DocuSP application has grown from less than 300mb to well over a GB more if a color machine is served.
There is no way to print without some form of interpreter. The beauty of the DocuTech is its dumbness. Put on a new controller and you update a 1992 machine to accommodate today's world. How many other 1992 copiers are out there?