gdgt

Anyone know?

if you mean, whether the Cowon S9 supports Apple's proprietary audio format AAC or not, then the answer is NO.

it supports the following formats audio and video formats:

FLAC, APE (Monkey's Audio), MP3, OGG, WAV, WMA

AVI, DivX, WMV, XviD (h.264)

can it be used with MacOS? but of course. it works with any operating system with USB 2.0 support.

does it come with software for MacOS? no, it doesn't require any software to manage the content. just drag 'n' drop (copy/paste)

Um, DivX and XviD are practically the same thing, and XviD is NOT the same thing as h.264!

Does anyone know for sure if the device supports h.264/AVC ?

'Mac formats' are not supported. i.e. there is no support for AAC, H.264, MPEG-4.

Audio, since iTunes incorporates the ability to easily transcode AAC to MP3, is not such a big deal. Video is the bigger issue: Especially as even with the supported video formats, compatibiity is not guaranteed or that consistent in implementation. The machine ships with a Jetaudio license for Windows only, which provides handy transcoding capabilities should your video not play on the S9. There are transcoding tools on the Mac should you have a bunch of Quicktime files you want to dump onto the S9, but this is an additional large hoop you have to jump through for video. Thankfully, the S9 seems to be pretty compatible with many video podcasts out there broadcasting in XVid / WMV format - Revision3 seems to works fine for me for example.

USB Mass Storage Transfer *is* officially supported from the Mac on the S9, which means that you can transfer compatible media from a Mac using drag & drop, or if you're using MP3 audio in iTunes, through tools such as iTuneMyWalkman.

However there is a huge gotcha with the S9 on a Mac which makes it non-recommendable in any case, at least up til the current firmware release (2.41). Ejecting or disconnecting the player in fairly easily reproducible situations results in a non-recoverable corruption of the storage, leading the player to be unusable until it is formatted - losing all your stuff.

Honestly, even if you were to set that aside, despite the nerd hype over this machine I don't think you're missing a lot. There are three things I can reliably expect with any Cowon:
1. That the firmware will always be half-assed and contain some sort of deal-killer bug.
2. That the superior sound quality espoused by the anti-iPod, Cowon-loving nerds out there will always be overrated.
3. That I will always buy every major release (such as the S9) and say "Gaddamn it, why did I sucker myself into buying yet another ******* Cowon?"

I'd look at the Sony X1000 instead - a more stable, better put together, more polished player - if you don't want a Touch and are a Mac user who doesn't want to run Boot Camp / VM's to connect a Zune.