There are no "codes" per'se to download. I have configured it through both the thick client and the web-based application. In both cases, it shows that the up and down arrows are defined by the database. So, they are not blank, like unidentified commands, they are supposedly in the database. I also turn every component off and go into Devices, and just power up the receiver from the on-screen command, and then go into the menu on the Denon, and once in, can use the left / right, but not the up/down.
The Up/down does work with my guide with DirecTV, so I know it is not a hardware issue.
As far as numeric codes for the remote, like back in the old days, there is nowhere in the Logitech software to enter in any codes.
I called Logitech, and after 5 minutes of verifying who I was, they stated that I bought it in 2010 and it would be $29.95 for support. I figure I will spend another hour or so on Google, and if needed, just buy a new Denon remote and train the Harmony. I am just afraid that if I pay the $30, I will end up with an answer like "buy the Denon remote and train the Harmony."
If anyone knows how to get this working without buying the remote, please let me know.