ok lets say u have Extended ACL
access-list 100 permit ip 192.1681.0 255.255.255.0 any
then u need to match any traffic from that subnet going to any distination with TOS DSCP ef
do the following
hostname(config)#class-map match-all voice
hostname(config-cmap)#match access-list 100
hostname(config-cmap)#match dscp ef
then u can apply it to whatever interface or globaly (to all interfaces)
the following link contain good details regrading ur question
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a008084de0c.shtml
good luck
please, if helpful rate