First you need to find a working setup code in the 8781, then check www.hifi-remote.com, for advanced codes(some can be discrete). Once the 8781 is set, then you teach the mx-500 the codes from the 8781, head to head, key to key. To enter advanced codes into the 8781;

1. tap the device
2. hold SETUP until the screen reads TIMED SEQUENCE.
3. press arrow down twice, until screen reads CONFIGURE
4. press SELECT
5. scroll down until the screen reads KEYMOVER
6. press SELECT, screen will read FROM
7. press SETUP once and release
8. enter the 3-digit advanced code, screen will read TO
9. pick a unused key