Originally Posted by lovinthehd
I think one of the major differences to consider is the 809 has Audyssey XT whereas the 818 has XT32. Plus am sure some other features, one other significant one I can think of is the ability to have a true electronic crossover for amplifying separate tweeter/sub-mid whether you're a speaker builder or otherwise, that's a pretty unique feature at this pricepoint along with the XT32.
The onkyo 818 has Audyssey XT32 and many software APPs which will be very useful for most users, as for the speaker tweaks, most wouldn't use them or worst use them all wrong. If your a speaker builder / tweaker this could be the AVR of your dreams. Plus onkyo is known for their high current amps which is why they sound better then most other mass market avr units...