I have a the Sony STR-DA2800ES - here are the instructions for changing command mode on the receiver and the remote as quoted from the manual.

1) Press Power to turn off the receiver.

2) While holding down 2CH/A.DIRECT, press Power to turn on the receiver.

When the command mode is set to “AV2,” “C. MODE AV2” appears on the display.
When the command mode is set to “AV1,” “C. MODE AV1” appears on the display

1) Press Power while pressing RM SET UP. The SHIFT button lights,and the RM SET UP button flashes.
2) Press the numeric button 1 or 2 while the RM SET UP button is
flashing. When you press 1, the command mode is set to COMMAND MODE AV1. When you press 2, the command mode is set to
COMMAND MODE AV2. The RM SET UP button lights up.
3) Press ENT/MEM.

The RM SET UP button flashes twice, then the command mode setting process
is completed