Via Mefiresu from the Russian Sonic community, fellow fansite Sonic Scene has received an MP3 file of what is believed to be the theme music played in the Sonic the Hedgehog (2006) TGS 2005 trailer.

[youtube]http://www.youtube.com/watch?v=k59_cHorjNk&feature=related[/youtube]
When compared to the faint music heard in the highest quality version (it was never made available outside of camera recordings) of the trailer on YouTube recorded by Kikizo (above), it does sound identical.

You can grab the full 4 minutes and 58 seconds long track over at Sonic Scene.

Thanks to Woun for the heads up!