Kind of has the symptoms of a incompatible print driver. You have confirmed that the printer redirection feature on your print server/RDP client is enabled. Otherwise you wouldnt get that gibberish printed out with your most recent test.
Instead of using a UPD PC6 you might want to try PCL5 or PostScript. Perhaps one of those drivers would have better luck. As you noted in your post you need to make sure that both the local client and the print server have the same print drivers available to them otherwise the printer redirection feature will not work.