controlling spdif volume?

  • hello i like to record all my tracks at -20 db. i bought a non powered kemper for studio use only. i was using xlr, but decided to use spdif and set it to got stack so i can record distorted track as well as di. with xlr i would turn the master volume till i got level where i needed it. the master volume knob does not effect the output. i went to output ans found spdif and started turning that, and it effected the distorted tracks but the di track was coming in at -8 db. so how toi control the di volume?