ALSA: emu10k1: more documentation updates

- Clarify the data flows. For SB Live! I fixed only the most obvious
  point ("from" vs. "for").
- Mention 7.1 side channels on Audigy.
- Be unspecific about the output DACs on Audigy, as lots of variants
  actually exist (see emu_chip_details table).

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230825222157.170978-2-oswald.buddenhagen@gmx.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>