The Onkyo S9400THX is a 7.1 surround system. Properly set up, it means that there are 7 regular speakers and a subwoofer. The three front speakers are about 50% bigger than the other four, and sound nice on their own. The subwoofer has a twelve inch driver, and is bigger than the microwave at work. This system is rated for 1000 watts.
It's about time I reviewed this, since the 90 day return period was long past even 90 days ago. As the model name suggests, it is THX compliant. It seems that the whole THX thing is about having the sound be as pure as the recording engineers intended it. To me, that's great. I'm not one of those people who turn up the bass so much that it registers on the Richter scale, although that is certainly possible.
The sound quality from this is stunning. You can really tell what is high quality and what isn't. This comes at a good time, as I have been reripping and looking for lossless versions of music I get and have for about two years. I enjoy listening to game soundtracks and orchestral scores on it. The opening score to Skyrim is utterly phonemenal.
I backed a Kickstarter a while back that was going to record and release all of Chopin's music for free. That gave me access to Musopen, a classical music repository, for a year. I discovered that this was their second project, and were doing it in the same way as their first. They had released that one even more openly, and in lossless format. This made me realize something about myself: I'm a wannabe classical music fan. I really want to be, I have the material, but haven't dedicated myself to it yet.
The downside is that it doesn't fit that well into a PC system. Surround sound is still kind of a hack in some areas, and doesn't help that sound itself is sort of an afterthought in game design. Far as I know, there's no John Carmack of sound programming. The vast majority of music is still two channel stereo, so filtering of some sort is needed to get it to come out more than about 3 speakers. The first generation surround sound interconnect is optical, but only supports 5.1 sound using specific codecs that you need to sacrifice a goat for to make work. That leaves HDMI, which allows 7.1 uncompressed PCM data to be passed to the receiver. The downside is that it needs video data present in order to pass sound. I've worked around this by connecting my second monitor to the receiver, and the receiver to PC, leaving my primary monitor unaffected. I noticed that something does chroma downsampling on the image, so it's not as crisp as using DVI or DisplayPort. There is some noticeable lag when compared to my primary display.
I've found a list of several games and the sound channels they support. I'll be honest: this system is the impetus of me playing the Bioshock games. It seems that a lot of popular releases use the Wwise system, due to the ease of it's development tools, but it's (formerly) limited to 5.1 sound. The good news is that as of October 2013, a new version came out, supporting 7.1 sound.
Since I've ordered it, Onkyo discontinued this model. If you can find one, don't let the $800-ish price tag turn you away. Get it and be blown away. You may have to look around for that price.