It depends what series of Onkyo you have.
My first Onkyo was a TX-SR608. My current is a TX-NR609. The "key" bit is the S or the N - as the "N" is network enabled
If you have a non-N series, you will need something like an iTach and some time to clone your remote IR signals, or (something I have not done) look into RIHD (remote interactive over HDMI) - which is (I suspect) the reverse of what I'm about to say
If however you have an "N" series amp, your life is MUCH easier (and Google is your friend)
Basically, Onkyo provide an Android/iPhone app to run your A/V receiver. You do however need to enable "Network Remote" support in your setup menus - and the default port is 60128.
Someone ran Wireshark to trap the protocol, but they are the same between amps - with new features being added. It's based (I believe) on the Integra ISCP (Integra Serial Control Protocol) and just works on Onkyo. The main list of IR and TCP codes are posted here :
http://www.awe-europe.com/ir_232.html - as this has both IR and IP codes listed you could program up an iTach if you convert the IR to Hex and fire it over TCP to your iTach instead of the Amp, which I describe below
Anyway, to cut a long story short, each command has a prefix (in HEX), and then an instruction.
The "prefix" for all HEX commands is 43 44 56 50 57 52 4f 4e and the suffix is always 0D
So, if you want to drive a PS3 hooked up to your BD/DVD input, you will need to use the Onkyo CDV command set listed in the IP command Excel sheet from the above link.
To power it on, you'd need to add "PWRON" - so you have "CDVPWRON". Except you need that in HEX.
So, use the Ascii to Hex website to convert CDV commands such as CDVPWRON to become 43 44 56 50 57 52 4f 4e
Remove the spaces and capitalise (4344565057524F4E)
Combine the prefix, command string and suffix 0x495343500000001000000009010000002131 + 4344565057524F4E + 0D so you get
The 0x is added by me as OpenRemote needs it.
Then create a TCP command pointing to your Onkyo IP (set it up on static!) and port, and click. Make a PWRON and PWROFF button to test/annoy your PS3
I wrote this up at my blog originally via https://sites.google.com/site/techbobbins/home/articles/control-your-ps3
For me, the ultimate win has been driving the PS3 from the Onkyo, so I can remove my PS3 Toothfairy IR2BT interface, and save some power. I was clued into this by someone pointing out that you could drive the PS3 from the Onkyo remote, and given I'd upgraded to an N series, thought "Righto, time to get upgrading"
I've asked Pierre & Juha if they want me to create a "bulk" command set to shove in the beehive, but haven't had a yes/no yet - at present my minimum implementation can power on/off the amp and PS3, change to specific inputs, turn the volume up/down/mute - and run the PS3.
SERIOUS NOTE : I have posted on this before - the Onkyo CAN overwhelm OpenRemote if you switch to NET/Internet Radio or DLNA modes. The TCP interface sends back all the directory info, or MP3 info, and this can be "a lot". I recommended a "send only" option for TCP, so you can send the command and ignore the response (as it should be on screen) - although in future it would be nice to put info on the OpenRemote display panel too - but right now it seems to REALLY clog it up :\
Normal TV/DVD/CD etc operation however is fine - although I do sometimes get an issue with HDMI (PS3) control which causes OR or the amp to keep connections open - but I have a manual (button pressing on the A/V amp) method to reset that if it happens to you.