My only problem with multi sub setups is that the DSP has to be 'just right' time alignment / phase + amplitude wise and it just cannot fix room decay issues.

Having a flat FR is good - but still muddy because much too long doesn't really help the guys that need to hear their LFOs automations, fast edits and notes, kick vs bass pumping, stereo effects etc.

In this case, headphones are still needed - so would the 'car and living room system check'.