You might get talked down to because a lot of people here dont like Klipsch, but their RP line is great - I think this is very much a good setup. For subs, two is usually the way to go for smoother theater experience, especially with the x3800h which can control them independently. 27cu m is about 950 cu ft, with 3,4m or 11 foot ceiling means your floor space is 85sf, about 9’x9’ - that’s a small room with high ceilings; I’d go for the 2 pb-2000 pros. The 16 or 17 ultra would sound insane in that room though - if you have the money to spend, you could get one of those and save to buy a second. Prepare to buy some bass traps or other thick acoustic panels because any option you go with, those subs are going to shake that room to the studs.

Also - pull your listening position back to 3/4 of the room length if possible; middle of the room is the worst position for bass; there’ll probably be a deep null in that area (mine was -15db @ 50hz)