Hybrid 5.1 ($1300( vs Ultra 3.1 $14.99 (and use my existing surrounds, Klipsch)
Not certain the exact difference in the subs, VTF4 MK4 vs ULS 15
The ULS is a sealed sub which is more for audiophiles and those who need decent performance but can't handle a huge sub. If you can fit a larger subwoofer, go for one of the VTF subs, they will get louder and hit harder, and would likely be more satisfying for home theater. I would also use the existing surrounds that you have if they are Klipsch. If you can accommodate it, go for the VTF15h. You might also think about dual VTF2s if you can't handle a sub the size of the VTF15h.