Hi there, we have exactly the same printer. We solved the problem by having an older mac running on os9 attached to our network, & using this as a "print server". We set up in OSX a dummy plotter & then always save/print our plans as "save PDF as Postscript..." in the print field.
Once saved we go to our old mac & print thru the original HP print software. It sounds a bit complicated but it isn't too bad, sometimes it's even better - you can always throw the print away before you print if you realise there is a mistake.
We have got all the programmes if you need the let me know. Good luck...