Sub Question. One higher quality sub or two lesser quality? (Rythmik vs HSU)

violins playing in the background... :)

for 2 channel stereo listening -- it isn’t about the amount of bass

it is about distribution of the bass and how it matches/mates w your speakers and room

two usually work MUCH better than one if the room is of any meaningful size

suggest you consider older, relatively inexpensive Rels... use high level connections - should be able to get two for just around a grand