Hi,
If ASA is already receiving prioritized packets then ideally there is no need to doing any QoS on ASA.
However you can still read more about it at :
https://supportforums.cisco.com/document/7011/asa-qos
http://www.cisco.com/c/en/us/td/docs/security/asa/asa84/configuration/guide/asa_84_cli_config/conns_qos.html
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Pulkit