I have the sealed box, with no ports. This gives a more controlled response at the expense of extremely low bass. Don't get me wrong, there is a lot of very, very low bass, it is a massive driver after all. The ported version goes a tad deeper, has more punch and volume but has a slightly more uneven response. I guess what I'm saying is I don't know about bunging and unbunging the PB4000 as it isn't a feature on my Sub. But the app allows for tailoring between movies and music etc, so can be adjusted from your armchair. It also controls level and several other features. The rear of the sub has a lot of adjustability too, but most of it is covered in the app.
You could get a PB4000 and see what you think. If you like it then consider a second one, if not return it. It is quite a beast. I don't know how loud or good, your old Kef was, but I suspect you will be more than pleasantly surprised by the SVS. I was amazed at the punch compared to my old Epos sub. I'm pretty sure you won't be disappointed with an SVS sub, they are superb and the whole range gets glowing reviews.
Here is a SB4000 review
Here is a PB4000 review