If you have all midi filters activated the Pa50 should only receive key on/key off messages. Maybe the PSR-3000 is also sending messages on the Pa50 control channel that is used for selecting perfomances etc. Make sure that no MIDI IN channel is assigned to the control channel (page 127 in the manual). Actually it would be best only to have one channel active - the channel that the PSR-3000 is using to transmit your playing.

I have no experiences with Bome's Midi Translator, but I really think that you should be able to get it working without a PC. I did something similar on my Pa60 a few years ago.

Kind regards,
Tommy