You can stop the channel by writing a 0 into the  audxen  bit at any time.
However, you cannot resume the output at the same point in the waveform by
just writing a 1 in the bit again. Enabling an audio channel almost always
starts the data output again from the top of the list of data pointed to
by the  location registers  for that channel. if the channel is disabled
for a very short time (less than two  sampling periods ) it may stay on
and thus continue from where it left off.

The following example shows how to stop audio DMA for one channel.

STOPAUDCHAN0:
        LEA     CUSTOM,a0
        MOVE.W  #(DMAF_AUD0),dmacon(a0)