You need TM Companion on a compatible PC/Mac and be connected over USB in order to update the DM's firmware. However, you may not be able to load firmware with that message popping up prior to full boot.
Did you just get this desk, or is this a message that has started popping up? If you haven't tried to go into the diagnostic menu, I would try to do that, to at least run every test on it. Ultimately that message may mean that DSP chip (or chips) are failed or failing, which a firmware update may not fix if it's a hardware level fault.
Do you already have firmware and software (TM companion or the full service manual set with everything but beta firmware)?