pcm_setvchans
err = pcm_setvchans(d, direction, vchancount + 1,
(void)pcm_setvchans(d, PCMDIR_PLAY, num, -1);
(void)pcm_setvchans(d, PCMDIR_PLAY, 1, -1);
(void)pcm_setvchans(d, PCMDIR_REC, num, -1);
(void)pcm_setvchans(d, PCMDIR_REC, 1, -1);
int pcm_setvchans(struct snddev_info *d, int direction, int newcnt, int num);
err = pcm_setvchans(d, direction, cnt, -1);