Hi, Wotski
Without wishing to throw a spanner into your carefully considered decision-making works(!), have you considered a REL sub? I have a REL R-218, which is awesome for music. Some of their other (bigger) subs like the R-528 may suit your needs better, with lower frequencies and passive radiators to increase the volume of air shifted. I went with the R-218 as it's only for music, and it sounds great - very fast & musical cpmpared to some others I tried.
Although the specs suggest a higher min. frequency than you metnion above, REL subs are (uniquely?) designed and tuned to be placed in the corner of a room, so the bass response is much 'bigger' and more natural than some other systems. One additional benefit is that they come in white, too...!
www.rel.net
Good luck!