I was able to generate hex codes that worked for my URC MX-980. I used this RC5 to Hex utility [Link: remotecentral.com]
along with the command codes in the first post (actually used an Excel file posted to AVS Forum) and specified System Address of 19 as mentioned above.
I'll see if I can find a way to post the info. In testing the codes, I found that some of the modes are incorrectly labeled and one of them is missing. Oddly, Power & Mute work but they only work once for some reason. In other words, if I turn power off, I can't turn it on. If I mute, I can't unmute. Learning from the AMBEO remote works properly though. The info I'm looking to post will include those notes as well.
EDIT: Not ideal but I've shared it via my Google Drive:[Link: docs.google.com]