One point in favor of the sb3 is that you can get digital room correction for free with inguzaudio, althought I think you have to jump through some hoops to get it to work on the mac.
One point about flac vs alac: they're _lossless_, so, assuming you got an ok rip, you can transcode them back and forth as much as you like without any loss of information. Not sure about the mac, but on the pc, you can do bulk transcoding of whole directory trees pretty easily using dbpoweramp (it takes a while, but can be left to run unsupervised). So the upshot there is, really, that it doesn't matter too much. If, for whatever reason, you don't like one, you can always switch to the other.
Another point is that you can also always get your wav file back, if you so choose. So there's really no reason to worry unduly about using either flac or alac. I've seen people claim that somehow "there is no such thing as lossless compression" (not on this thread, happily). Not to put too fine a point on it, but such people have no real idea how compression works, and are simply spreading FUD.
The only reason I switched from alac to flac was that, with the inguzaudio/slimserver combination I was using about a year ago, I got "clicks" at the beginning of alac tracks (as far as I remember, due to a bug in slimserver). The only caution I would give about alac is that you are depending on a company who owns a proprietary format never to do anything really nasty to it (given the current environment wrt drm, etc, who knows whether that's naive or not). With flac, the whole thing is open, so even if it was decided to "do the wrong thing" with flac in some way, it would be possible for someone to fork the project.
