The DX7 Pro is a high resolution device, so I would think you want a power amp that will let that carry through as much as possible. I'm running an SMSL M500 as a DAC/Preamp, so I have some familiarity.
I've never heard the Neat Iota, so I did a little searching. I'm at least somewhat familiar with the 4" Peerless midwoofer (or at least the version available to the DIY community), and read that it crosses to the planar tweeter at about 5 kHz, which is probably what I would have tried with that pairing. My Rhodium design is similar in several ways (a 4" two way with similar size, bass extension, and a ribbon tweeter). I would expect that Peerless driver to have a somewhat warm and forgiving character, and the tweeter to give pretty clean, delicate highs if the design is executed correctly, which the reviews seem to indicate is the case. Your challenge with the Iotas is low sensitivity, so in addition to the consideration that you want an amp that measures well, you also need a fair amount of power.
My recommendation is something based on Hypex NC252MP. Examples from March Audio and IOM have been reviewed here. There is also a US based outfit, Vacuum Tube Values, that sells them on ebay or through there own website.