I have had sort of the opposite experience from sledwards. I started with 2 sealed subs (massive Paradigm Defiance x15 subwoofers) and then built the triple servo subs. What I was expecting was that the servos would have more speed and detail, but I thought that the sealed subs would have more punch. In my experience, that was not the case. To me, the servos have just as much punch as the sealed subs, if not more. What is different is the pressure wave in the room. It's not so much a difference in how it feels, but I can hear it... in my walls. My sealed subs shake the house, and I can hear the drywall shifting around when the bass is loud. The servo subs don't do that nearly as much as the sealed subs.
My opinion, after hearing the difference in my room, is that adding a sealed sub or subs, would only muddy the bass. I have done a bunch of AB testing with the paradigm subs and the servos, and on all songs the bass is dramatically better - in every way (apart from the "punch", which in my opinion is about the same) and now there are a bunch of songs that I never used to like that now I find amazing. Switching back to the paradigms it sounds so absolutely atrocious that I can't listen to it.
What I'm not sure about is you don't have a normal sealed sub - you have sealed servo subs. What I would try is listening to a song that has incredibly fast bass - like Thundercat "Uh Uh". If you hear separation in the bass notes then you're doing well, if it sounds at all muddy or smeared, you are only going to make the bass worse by leaving those subs in your system after adding the open baffle servos. Just my opinion.