Great info!

Is there any chance you could rta the sub channel directly off of the subwoofer outputs from the ML amp? That curve looks awfully odd for a 8" free air sub. I am just wondering if the lc2i is doing something to the bass. I only used a tone generator and my ears, but mine certainly didn't have any huge bumps between 40 and 100hz. I was getting a pretty quick Rolloff below 40, but I assumed most of that was due to the limitations of my small sealed enclosure. I am using the stock crossover points, and if anything, I have too much between 100-120hz.

 

I also thought that curve was funny. But I thought about it a while and it made sense. I suspect the Fs of the ML sub is in the low 30's so there's a steep rolloff below 30hz. It's also clear that the ML system focuses on front stage imaging so it avoids any rear output above 100hz by steeply rolling off starting at 50-60hz. This should be fine if the front woofers can provide good output down to 60hz. Which they seem to do just fine. All speakers were still connected when I ran some sweeps and I could hear the transition from the sub to the fronts as it moved past 60hz.

I suppose I would need to try a different line-out converter if we were testing a hypothesis of the LC2i creating that curve. I dont think this is the LC2i's fault. Here's why:
A. I suspected the accubass might be causing this so I had the accubass function of the LC2i essentially disabled.
B. To make sure, I tried this at various volume levels. The curve was the same every time.
C. The LC7i has the same accubass function and I was able to apply it to the summed output. I had to move the threshold **** to half-way to see any effect. See the image below.