Can anyone give me a quick rundown on how Onkyo model numbers work? I mean, how far up the model number range do I need to go get THX? I'm looking for an AV amp to run my Acoustic Energy speakers and there are so many I don't know where to start. The 8 series seem to be the real good ones, but a little trumpy for my modest budget. I'm looking to spend around £300, but am happy to go second hand. Thanks.