I tend to agree. After listening to this preamp for a few days, I'm building one of these now for my personal use and given the speakers I use only go down to 40hz anyway, I'm going to use a compromise cap in that output position, likely a 4.7uf or maybe even a 2.2uf. I threw that 6.8uf in this prototype just to ensure this low frequency roll off a) could be eliminated and b) prove to myself this one cap was causing it.
