akilgore:
1) Are you sure you are talking about discrete codes, and not a toggle bit on the IR (the way you describe the functionality, it sounds more like the latter)
2) assuming it is sending discrete, the truth is for most other manufacturers it does not work that way. the way it works is the remote itself only knows "power" while the equipment knows "power", "on", "off", you can easily get the code for power (from the remote) but you have to search for on, and off, or someone needs to tell them to you.
The problem is not one fold, but two fold. like John said:
Those commands are probably available thru the
serial control port of the Marantz plasma.
The Pronto, HK.... created a middle ground between the low end remotes and the high end controllers. High end controllers (like Crestron, AMX....) use RS-232 to control the equipment. They do not need discrete IR codes, so manufacturers assume that either you use the original remote or RS-232 so they add discrete serial codes and don't care for discrete IR codes.
so what I am trying to say, is yes the low end does not care for discrete IR codes, but the high end does not care either. So in the middle where we stand there is no solution and no one else cares.
