I looked into this myself a while back and the answer from Meridian was No, because of space limitations in the 5 series casing primarily. I think that's fair enough, especially when you consider that the HDMI format did not exist when the 5 series DVD machines were produced.

There is a Dutch company, JVB, that can modify a 596/598 to deliver an SDI digital output which you can then scale up & convert to HDMI with the appropriate scaler.

However, it's far cheaper just to buy an HDMI equipped DVD player than go through all this hassle!

Regards

Paul