John, a few years ago some of the Hsu subs had a separate fixed high-pass filter on the speaker level outputs which could be connected to the mains. The present models have just a straight-through full range connection to the mains(if used instead of a direct connection of the mains to the amplifier).
Since the M22s are therefore having to run full range, a 60Hz sub low pass(if the settings on the Hsu control are accurate, which they may not be)probably is reasonable in trying to get a good blend without receiver bass management being available.
