The Mac 500 has 4 operating modes that take different amounts of dmx channels with Mode 4 taking more than mode 2
To find out what mode it is in go to the PSET category off of the main menu and it will show the mode there
M4=Mode 4
M2=Mode 2
You can find out more information about the different modes on page 14 of the user manual
GF = gobo fixed, GF = gobo scroll. The former allows only full frames and snaps between them, the latter allows one to roll from one to another. This is set in the fixture under SPEC/Gobo/ Fix OR Scrl. Applies only to the non-rotating wheel.
Mode4 adds two timing channels that most people don't know how to use properly. Unless you're doing very slow moves over a long distance, you'll never need them.