The cookie made by pulse (/var/run/pulse/.pulse-cookie) has not the mode 640 and the group is not pulse-access. In consequence, clients applications (mpd, paplay, ...) cannot read it if 'cookie-file = /var/run/pulse/.pulse-cookie' is put in /etc/pulse/client.conf My pulseaudio is media-sound/pulseaudio-0.9.7, freshly compiled yesterday. Reproducible: Always
When using system instance, pulse-access group presence is the only requirement for access, the cookie is not needed at all. You changed your client.conf for whatever reason, you caused it not to work as intended....