I used to program Prontos and the Marantz Pronto-related remotes. There's software here on RC that will allow you to program these devices, and it should not be too difficult or costly to get one on ebay.

You can learn the codes from your remotes on the Pronto, then use the editor to see the individual Pronto Hex codes. There's also software here that will let you enter a few Pronto codes and will then generate the 256 codes of that particular device.

That should get you a complete set of possible codes. It's then up to you to try them out. There's a danger to that approach, but I've only heard of it on TVs: if one of those commands puts the device into a Service mode, you then have to figure out how to get it out of the service mode to use it. In other words, you might brick it.

It's worth a look, though.