@mijostyn I agree with you. To me, his space needs 2 subwoofers (at least at this point it sounds like they do). Frequency tests show 130hz and lower just drops like a stone. Example : 1000hz is at -24db, and 80hz is at -44db at the nominal listening levels. I need to be careful though, father is VERY sensitive to bass and can be irritated instantly if he thinks/feels like it's 'boomy' or loud. I have heard a ton of systems with extremely articulate and impactful bass-you hear the detailed pluck or hit of bass, but you also feel it's impact and weight. With his system currently, it's just mainly the audible portion of the note/pluck/hit.
However as you and Erik have noted the greater issue is room echo/reverberation/decay and the corresponding impacts on phase and timing of the frequencies. Like you mentioned, we need to break things up, diffuse and absorb in general (there's nearly nothing in the listening area from the chair to the front wall-just the speakers. Just monkeying with a handful of panels and some ladders with blankets in key spots against the walls is showing how dominant the echo is in the room, and how it's coloring and even creating a cancelling or veiling of ACTUAL recorded room qualities \ instrument qualities, etc. He's able to hear at least some improvements, but he's also very sensitive to changes so just easing in on things.
I think I have things calculated and types of panels he should get and install, but I wish there was like a diffusion/absorber kit you could rent to test out!!!!!!!!!! I want to be sure to preserve the immense sound stage and depth he has, but tame the echo reverb, and "warm things up" so there's more feel and presence to the sound.