The Bijou 2100, 3100, and 5100D will always respond to CEC commands if connected to an ARC/eARC device via an HDMI cable and set to the eARC input.
If the Bijou is in standby, it will turn on when the TV is powered on, and set itself to the eARC input.
If the Bijou is already on but set to a different input, it will set itself to the eARC input when the TV is turned on.
While the Bijou is on the eARC input, it will respond to volume commands, mute commands, and power off commands from the TV.
When the Bijou is not set to the eARC input, it will not respond to CEC commands. You will either need to use the Bijou's factory remote, a control system, or use the source's controls to change the volume and mute state on the Bijou.