The one other issue with RAW printing from Windows is that there are two supported models either "RAW" or "XPS_PASS". Can you check your driver model and version and share that.
In the meantime, I will write a new Print server that uses GDI that would be guaranteed to work. Would you mind providing some testing support as I only have limited printers on hand and of course they all work, so if you would not mind that would be great.