The SR-508 has F:x so no fan. There's a number on the left that's usually 000 but sometimes changes to 001 or something, do you know what that is?
I have 10cm on each side of the receiver, but it's enclosed, with a 140mm fan in the back which should move a fair bit of air through. Without the fan it gets much hotter to touch. I have Wharfdale Vardus speakers, a 5.1 system. I run the amp at 1/2 power (40/80) during movies.
I think I'll get a 140mm or 200mm computer fan, put rubber feet on it, and wire the fans all to my variable voltage power supply. Even with a little case and connectors it'll only cost $40 or so, and it may extend the life of the amp. I have a power saving thingy that turns the power completely off when there's no power draw, so it'll turn off when unused anyway.
Thanks for the thoughts and help :)