Bit-Matched is the term we're all looking for, it only matters for S/PDIF output (as it only influences the master digital clock), and if you enable ASIO, this all means much less (as you're going straight to hardware, thru the ASIO driver, in other words, you're crying so hard and so long about kmixer under XP that you're giving up functionality for no reason)
audio creation mode does NOTHING for soundstaging/imaging, and contrary to mythical belief, does not disable CMSS/EAX/SVM/Crystalizer, unless you're talking about default settings (the myth that it expands soundstage/positioning/etc, sure it does, just like the Tice Clock improves your stereo exponentially
)
there is no "music mode" with CMSS3d "which boosts bass and stuff", this is pure fabrication of the collective imagination of head-fi
/waits for someone to flame me for not agreeing with trendy opinions based on pure myth
now lets talk reality:
if you don't have a headphone amplifier, you want headphone mode enabled, why? because it tells your card to kick the gain up a bit, this drives the hp's a bit better, so you'll probably wanna worry about that before you get into using the card as a preamplifier with zero power amp
secondly, bit-matched/etc does squat if you're going analog, the card doesn't perform SRC unless its told to do so (no Creative board since Audigy 1 has had SRC issues (waits to get flamed for this too
)), so theres no problem there
thirdly, Crystalizer/CMSS/EAX/SVM sometimes "help" music, really depends on the listener (its your ears, why not play with it? who cares if trendoids don't like it), SVM is a software compresser, EAX is environmental DSP effects (like Yamaha's Scene DSP), CMSS is similar to Dolby Pro Logic/Headphone, and can do some pretty neat things with positioning and imaging (especially in games and movies, when set to headphone mode)
Crystalizer is the DSP plug-in thats likely getting the rap as "boost bass and stuff", it applies an EQ curve with some other presets (its basically Creative's in-house response to BBE), some find the effect pleasing, others don't, and it will vary track to track (just like BBE)
oh, and if you're wondering where the majority of this information comes from (at least in terms of what settings do, how to enable/disable them, etc), take a gander at your user manual, eh? (waits to get flamed for reading the user manual)