I think pulseaudio might do the trick. Its in the repository as you suggested.
I added pulseaudio volume control, also in the repository. But the controls don't work.
According to slackbuilds.org, I need libatomic_ops for pulseaudio, which is not in the repository.
Also, according to slackbuilds, I need a pulse group:
Pulseaudio will need a pulse group/user to run. You can add one with
# groupadd -g 214 pulse
# useradd -u 214 -g pulse -d /var/lib/pulse pulse
However, #groupadd -g 214 pulse brings on:
root:# groupadd -g 214 pulse
groupadd: GID '214' already exists
root:# useradd -u 214 -g pulse -d /var/lib/pulse pulse
useradd: group 'pulse' does not exist
So, I've got some learning to do when time permits.