If you go to the NHT web-site , you will see reviews of the PB10 sub-woofer paired with other NHT speakers. You should be fine with the all NHT set-up.
I too have used the SW2 sub and MA-1A amp with four superzeros and matching NHT center with good results. But with the price of a used SW2(P) and shipping you can get into a 10" HSU or SVS for not much more money I would guess. Not having heard a 10" SVS or HSU, I have to believe it would be an all-around better sub then the SW2P, with a tigher sound (less boomy) and being able to go lower into the hz's.
Might also want to check the HSU STF-2, as I see they have dropped the price to $399, most likely in response to the PB10.
Good luck and please report back how you like your new sub with the NHT's.
Another thing to think about for your system would be to upgrade to some used NHT Supertwo towers. The towers go down to around 35hz, and such, are much easier to intergrate with a sub, and are much more enjoyable to listen to in 2 channel listening. They are also a sonic match for your existing superzeros.
Just to report back... the SVS PB10-ISD complements the Superzeros well. No standing waves or noticeable gaps in bass response. Crossover set at 90Hz (I would go higher if I could). Overall, I highly recommend this setup for someone in my shoes, i.e. someone with less than $800 to spend for subwoofer, center, front, and rear speakers. Thanks for the posts.