I remember reading a similar question a couple weeks ago, and I believe you can use the front outputs as variable outs (acting as a preamp). Only thing is that a) you'll need to change cables between using headphones and interconnects, and b) you'll need male XLR's to connect to the front of the BDA (unlike female XLR's you'd normally use with a preamp) - so either cables terminated that way, or using a male-male XLR coupler.
Don't take my word for it though
I am working from memory - double check with HeadRoom to be safe
Don't take my word for it though