Volume CC7 should only be used to set relative volumes at the beginning of your track. This can be set in the Track view as well as the panning. You must enable CC7/CC10 in Options in the GPO player. I recommend not enabling this option and only adjusting volume and panning in the player instead of in Sonar. This will preserve the level balance programmed into GPO. For example, the strings are in the -6.0 db range as well as the percussion but the brass and woodwinds being much louder than the strings are usually between -17 db to -12 db. These level settings keep GPO from overloading the audio in Sonar.
If you do volume settings in Sonar, then do not set them higher than 65 or you will overload the audio and cause clipping. You can set it a little higher if only using a couple instruments. Somewhere around 81 is 0 db, so anything higher than this will cause some nasty clipping.