If you aren't hearing anything below 80 Hz, that would indicate a defective USB input to me. I would contact Schiit about that. No serious audio company would send a piece of electronics out into this world with that sort problem with one of its inputs. There is a problem somewhere (the DAC USB input or your USB source) that needs to be solved.
Maybe if I were to get another DAC, but I like the Bifrost, don't wanna send it out for repairs even if it is defective. Maybe get a new USB receiver or something (take advantage of the modular feature that was marketed so hard) sometime in the future.