My topic on hifi siren recording:
http://airraidsirens.com/forums/viewtopic.php?t=3118
As long as your original uploaded video file is done in stereo, I think youtube will also recognize as stereo. Youtube used to be only mono, but that changed with that video of the 2t22. I'm planning upload my next siren audio recording onto The FreeSound Project. I will also upload the video to stage6.com, since it doesn't compromise on quality, sound and video, like youtube does. stage6 also allows you all to download the video, without the need of a youtube ripper like tubehunter.
I was in the market for a professional sound recorder about a couple weeks ago. I just bought a Roland Edirol R-09.
http://www.edirol.net/products/en/R-09/specs.html
I will be using it to record on test day coming up here on the first working day of the month.