I thought Apple’s supplied Lightning adapter had a pretty low output impedance to begin with, I think the IEMatch would only serve to widen the dynamic range there. I use my MD+ with an iPad Air 2, without the IEMatch in line I can only turn it up to 4/16 before the volume is too loud, with the IEMatch on ‘High’ that goes up to ~8/16 and when I set it to ‘Ultra’ I can push the iPad up to 12/16. That’s using the built-in headphone jack, though.
Another avenue you could look down is Null Audio’s Capri DAC cable, they do lightning to 2-pin if you don’t mind sacrificing the ability to use the Plus with anything else
Interesting, I'll have to check out Null Audio's cable selection. Do you find you hear minor hissing once you start playing anything with sound on your iPad air 2? (Without the lightning adapter) Once I turn off the sounds there is some minor hiss but goes away after a second.