switched from my phone... sorry for the second post.
Multiple subs work best if they are matched. It is possible to mix different models or brands, but can also be problematic to set up properly.
If you want to upgrade and can... check with SVS about returning the 1000, or just jump in and order 2 more.
I personally have been using an underpowered and undersized sub for years in a room ~8000'3. With an old onkyo HTIB along side speakers the size of kleenex boxes. They can work. But really, I would need 2-3 15" bohemeths to maximize bass in that room.
So couple quick slightly educated recommendations, in no particular order:
a) return the 1000, buy 2 pb12nsd now. and maybe another next year if you think you need more even better bass.
b) just buy two more pb 1000s now, or one now and another next week.
c) return the pb 1000 and straight up upgrade to the largest single sub you can allow yourself to afford that will trully handle your room... so maybe even a PB4000? then save to buy the second 9mos-a year down the line.
How big is your room?
And like I said... I lived with under-powered and under-sized bass for years. if that sounds good to you now... just increase the number.