I also own an ONKYO 609, Just want to share what I did for my receiver, so far ok naman.
All items from CDR-King
I bought a Notebook Cooler for 380php, there were cheaper ones but I chose this model because it had 2 big fans and its color was black, which would make it almost invisible on top of the 609. This notebook cooler looked the most classy among the others available, well it was one of the most expensive.
I got a USB adapter for 50php in order for me to be able to plug it in a 220 outlet.
Since the USB cable attached to the notebook cooler was really short, I got a usb extension for 80php, so it would be able to reach the 220 outlet.
I went home, assembled it, put it on top of the receiver and so far, it works fine, does it job of cooling the 609, looks "cool" too.
Hope this helps.