Correct, not at the inputs but you can adjust levels via the webui whilst in use. Alternately, you could set up a speaker profile with selected speakers boosted/cut and create a virtual input with it. IE, blueray movies normal, blueray movies center+3 dbNo, it does not have level adjust for each channel (L/R/C etc..) at the inputs.
The input level adjust affects all channels together for the chosen input.