The original Action Replay firmware takes over the boot process before the Satiator can hook in, so it prevents the console from booting directly to the Satiator menu. There is a work-in-progress patched firmware which works around this issue, as well as adding some new features - like the ability to press A+B+C+Start from a game's start screen to return to the Satiator menu.
The latest patched firmware can be found here.
The AR patch is open source; you can find the source code on GitHub.
To access the Satiator with an AR cart installed:
The system should then boot into the Satiator menu.
In order to flash the patched firmware on to your AR:
ar_patchedxxx.binis on your SD card
ar_patchedxxx.binin order to flash the new firmware
When you power cycle, the new patch will be active.
If the AR tools report a flash ID error, you can wiggle your cartridge to help it seat, and try again. If you can't get it to work with menu 60, try menu 59 - there were changes in flash ID detection. These will be resolved in a future release.
This section describes the AR functionality as of patch version 3.
When you power on the console, it will display the SEGA logo, then boot into the Satiator menu.
If you hold A, or if no Satiator is detected, it will boot into the Action Replay menu, so you can still use the AR with discs.
A+B+C+Start can be used to reset to the Satiator menu from in-game. The Sega standards say that games should return to their main menu when you press this combo, and if you press it again, that they should exit the game, so you will need to press this twice in most titles. For this feature to work, you need AR patch version at least 3, firmware at least 154, and menu at least 60.