I have been looking into this and the issue here is that (as far as I am aware) some of these earlier remotes including the RC-898 require 5v which they normally receive from bus power on the 15 pin connector. I believe it would be possible to use them with the X-48 but they would need to be powered somehow either by adapting a custom cable to send 5v over the otherwise unused 15 pin cable or adding 5v power some other way.