I own the modified SA-220 which I think the upgrade is considered to be the NP-220. It uses (2) 6SN7 tubes in the amp versus the old (4) 6DJ8 tubes. Rated at 220 wpcs and I think 380 into 4 ohms. I lent the amp to a friend at an audio rave and he told me that the amp drove a pair of Maggies very well. It was the best of the amps that they tried then. Not sure what other amps where there.
So I would think that the NPS-400s would do an equal or better job at powering up the Maggies.
So I would think that the NPS-400s would do an equal or better job at powering up the Maggies.