I have an AVIC-X920BT with XM radio. Does anyone know if there are voice commands to switch stations or presets? Something like "play XM preset 1" or "play XM 20 on 20"? The manual didn't mention anything about such commands so I'm worried there are none ...but I'm hoping someone can tell me I'm wrong. Thanks!

No that command is not available. To see a list of available commands, please see page 181 of the Manual.