The WS-X6548-GE-TX and WS-X6748-SFP cards do not support MQC (Modular QoS CLI).
Only a few cards on the Catalyst 6500 support that (usually referred as WAN cards).
The Catalyst 6500 supports a subset of the MQC.
You need to take a look at the Configuration Guide for your Catalyst 6500's IOS version.
Example:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/qos.html#wp1465326 You will have to configure LAN QoS commands for those QoS mechanisms that are not supported via MQC.
Example of LAN QoS commands:
-- Global --
mls qos
mls qos map cos-dscp 0 8 16 24 32 46 48 54
-- Interface --
mls qos trust cos
wrr-queue cos-map 1 1 1
wrr-queue bandwidth 30 70