I use an old android phone to do something similar with my Yamaha AVR. Althoguh I could never find the RS232 commands ( the user manual says it supports commands, just wont say what they are. Need to be a authorized distributor or service person i guess!!). So instead I use the ethernet connected IR transmitter supported by openremote which sits in front of the AVR. I use the IRtrans brand(see details on openremote.com). works well.