I'm not sure what your target is for surround sound, but as far as Logic and Compressor goes, the workflow is as follows:
In Logic, you work in a surround project, and bounce your audio tracks to discrete L/C/L/Ls/Rs/LFE channels. That's 6 audio files. In Compressor, there is an "Add Surround Sound" button at the top of the job window. Clicking that will reveal a matrix in which to drag and drop your 6 files. Then use one of the Surround settings (like Dolby Digital Professional 5.1 preset), submit the batch, and you'll have a file (with a .AC3 extension) that can be used in DVDSP to author a DVD with surround sound.
You mention that you don't want a compressed format. It might interest you that the highest bitrate you can use for AC3 is 448 kbps. In relation to MP3, most people's perception of quality loss is at 128 kbps, while others with "better ears" top off at 256 kbps or 384 kbps. Consider the fact that the majority of Hollywood movies on DVD, if not all, use Dolby Digital encoded around 384-448 kbps. Some of those have a higher-fidelity, alternate DTS sound track which is
still compressed at 4:1. For true, uncompressed audio, you're looking at stereo PCM--no surround. There is Dolby TrueHD, which uses a lossless algorithm, but this is in the realm of Blu-ray discs.
Again, how you encode your surround stuff depends on your target. While MP3 surround is an option of delivery, compression issue aside, your audience needs a playback mechanism for this format. The best you might get across is a perceptual surround playback on headphones, since most people who download your Surround MP3 files will be listening on their computers. You asked if iTunes would play AAC/MP3 in 5.1. Well, I can't tell you about AAC, since I've never dealt with that particular format when it comes to surround, but Surround MP3 files are supposedly backward compatible, so they can be heard on standard MP3 playback mechanisms (software/hardware). You won't hear the surround aspects of them, though.
Anyway, I've made a lot of assumptions about 5.1; and there is a lot of missing functionality (it seems) in OSX, in general, with regard to end-user consumption of 5.1 mixes.
Most certainly. I think that if the desktops come with a built-in optical port, there should be more support for surround audio playback through the computer. Admittedly, I haven't looked too far into this since I don't have a surround setup other than via discrete 5.1 channels.
