Hello, I am currently working on a backend that should handle this scanner. There is an experimental version you can get at http://stef.dev.free.fr/sanerts8891/index.html . It is currently untested for the UMAX Astra 4400, but it should work (minus bugs...) . I'm about to finish complete support for the HP4470c which is based on the same hardware. I think this will be finished by december. If you need some guidance on how to install and test, let me know.
Regards, Stef