I called Bogner and talked to Reinhold about this same issue last month when mine arrived. He said this is normal when using the loop in series and that I should run it at line level and boost the signal coming out of my rack. He also said to max the gain pot on the loop.
After maxing that out, I just bumped up the output at the end of my axe fx chain and I was able deal with the volume drop. I was able to do the same with my pedal board by putting my Tech21 Qstrip at the end of my chain and boosting the level.