RCVR/1308 is a combo code, so therefore it doesn't support advanced codes. Either 0308 or 0309 would have been the right codes to use, as these do support advanced codes, but they are not present in the URC-8811.
So, you have two options:
1) The non-JP1 answer is to learn the numeric buttons from your original remote, however, the URC-8811 has a memory capacity of about 24 buttons total.
2) If you get yourself a JP1 cable, you can add a new code that has the numeric functions programmed to the numeric buttons.
Rob
http://www.hifi-remote.com