This is mainly for reference, but it may help you in any case. I don't have experience with the newer standalone URC remote other than reading a bit in instruction manuals and reviews.
In CCP (which obviously isn't for setting up an MX-450) the codes for that receiver are:
So URC has a lot of data for Onkyo receivers (those database references are used by a large number of Onkyo model numbers of course).
If there's absolutely no way to reference additional sets of codes from the MX-450's LCD or if those codes are simply not part of its internal database, then you're likely going to have to learn them, either from the original remote or from another remote that you can program from a PC with the correct codes (from URC's database or by manually inputting the codes as it's easy to get the Pronto-format HEX for them).
