Well I'll jump in so that there is at least some reply, even though I am most definitely no expert in this area
Two things jump out at me looking at your specs versus the game requirements. The first is your audio device. Isn't an ATI HD audio device some kind of home theatre arrangement, pumped out through an HDMI port? Can you set your default audio device to something else (either a sound card, if you have one installed, or onboard sound), then get the game to inspect your system again? It may be detecting an audio device at the moment, and thinks it has passed, but maybe the game installer is more picky when push comes to shove...
Second, you are tight on disk space. Are you running an SSD? If so you may just be pushing things a little too close to the limit. If it's a conventional hard drive then it really is too close to the limit: you need at least 10% of drive space free for things to run nicely, but the install is only going to leave you with 2Gb free and I expect that is way less than 10% of the drive's capacity.
Just my £0.02 worth