Yes it is flat. My setup uses a M650 feeding a toslink 2.0 signal directly to a JL Audio VX800/8i for all mids, highs, center channel. I piggy backed an amp onto the VXi to power the stealthbox with a 10" sub off the VXi and the truck pounds. I'm using 7 channels on the main amp with the second amp handing the 8th which is the sub. The DRC knob is installed in the compartment in front of the cupholder and controls mid/hi volume, bass level and presets. Bluetooth connection for an iPad to adjust frequencies, presets, eq curves the whole deal. Freaking amazing. The ONLY thing I lost was front/rear fader since the 2.0 signal is left and right. If I really wanted I could setup a workaround through the VXi for fading but it doesn't matter to me. No line out converter in the world can ever compete with a pure untouched digital signal directly from the vehicle.
A neat thing is the DRC knob now controls the turn signal and other chimes so if I want silence I got it
I don't think you'll have the problem you had before.