Maybe
Intel's PDF will help?
IANAAG (I Am Not An Audio Geek), but I gather most of the love for the SBLive stems from three things- Creative Labs' "superior" construction techniques, the ability of the EMU chips to (co)process audio data, and the powerful MIDI support in those same chipsets.
Many "normal" people dislike onboard AC97 audio systems because they find them 'of poor quality' - presumably due to interference in the analog stages, whether on-board or on-chip. This depends a lot on your particular board and chip; when I was on my EPoX 8KTA3, I had to crank my external amp far beyond normal listening levels to hear any static or hum. A more basic problem is that, even inside Windows, it's hard to trick the single 'speaker' jack provided on most boards into acting as a proper line-level output. These aren't really AC97 problems; they're implementation issues. Meanwhile, SBLives have at least half-decent analog stages, and carry on the tradition of separate 'speaker' and 'line out' jacks, or at least have a simple toggle in the driver.
From there, you get into features that AC97 simply doesn't provide- *if* you have the right software/drivers, the SBLives can offload a lot of processing (for MP3 decode, effects, etc) from the main CPU. This comes in handy for three classes of application- what I'd consider "peon" apps (the audio players that come with the card, and allow you to select 'stadium' simulation or whatnot); audio libraries- presumably DirectX can take advantage of certain 'accellerations,' and support is claimed for whatever OpenAL is on Linux - for gaming, at least, some CPU offloading would occur, though 'quality' is probably subjective; and high-end professional tools, which no-doubt give real thought to accuracy, quality, etc. Meanwhile, MP3 decoding to an AC97 chip uses only a fraction of CPU time on any modern system, so it's not like you're totally crippled by not using a SBLive. (For gamers, offloading the decoding for game music does translate to a mildly increased framerate.)
MIDI support isn't a part of AC97 at all, while the SBLive has numerous highly-advanced features... none of which you'll ever touch if you don't use MIDI. For a pro, it's no-doubt great; for playing back an annoying tune on a Geocities page, it's.. overkill. (A software MIDI decoder comes with Windows, and Apple seems to have relied on them exclusively? during the '90s; I have no idea what they currently use for sound. Similar software can be wedged into Linux/*BSD.) I have to wonder how many (gamer/consumer) SBLive owners are using the Microsoft software decoder without realizing it, whilst bragging of their card's abilities.
The big problem (fixed with the Audigy?) is that all the snazzy features came at a price- all operations on the card were handled at a fixed sampling rate of 48KHz - meaning 'rounding errors' (more like framedropping/interpolation noise?) when going to/from (and worse, to/from/to/from/to ad nauseum) the popular 44.1KHz of CD audio. One mitigating solution has been to leave the output at 48KHz... which works fine for other SBLive users, but requires conversion when going to CD... and could show up other samplerate-conversion/'rounding' issues in things like FreeBSD's "vchans" mixing code.
