Did you try this website for the information you are looking for?
http://www.a4400.spb.ru/omni_pcx_4400.html It's a russian site but most of the manuals are in english.
I now have a copy of the R4.2 System documentation (technical manual) both as CHM and as PDF's. If anyone has an FTP I could upload to I would be happy to to upload the CHM file but it is 77Mb.