Columbus MIB 2.5 - Volume Control

Hi guys,

Bit of a weird one but here goes. 

I have a Columbus MIB 2.5 retrofitted with the 9.2" touchscreen. I have recently installed a complete audio upgrade which consists of an AudioControl LC6i, Alpine PDX-F6, 2x PDX-M12 amps and speakers.

I have all the amp gains set correctly with the use of an oscilloscope and it all sounds great. The only issue I'm having is the volume control or speaker level output control from the headunit. When increasing the volume from mute all the way to maximum, the volume peaks at around half way or 50 per cent of the scale. It's like there isn't much adjustability from 0 to 100 percent volume. I have used a test tone and measured the speaker level voltage coming straight out of the headunit and it goes from 0V through to around 2.9V all within the first half of the volume scale, then doesn't increase at all beyond that.

Depending on how I configure the LC6i / amp gain, this results in either the volume being too quite when maxed out on the headunit, or the volume being too loud at the minimum setting on the headunit. I can't seem to get a full range of volume control from the headunit as the speaker level voltage maxes out at 50% on the volume scale.

I hope this makes sense, it's very difficult to explain in words.

In VCDS, the infotainment is coded for "Sound System Internal" as my car didn't come with any external amplifier, just the standard 4 channel output from the headunit. Does anyone have any ideas of what I could try or how to get the headunit to use the full range of the volume scale?

Thanks 👍