Ok, so batch converting to PNG works to a certain degree... but, the process stops at 134 frames out of 176 (the sequence is actually every other frame, but that doesn't seem to affect things until this point.
Secondly this seem slightly less preferential to using multichannel EXRs, as it's going to create a lot of PNGs if I want to start using render elements in post, and possibly take up more disc space overall.
Lastly, does anyone know if it's possible to just do the tonemapping in After Effects? I'm guessing it would have to be done in a Linear sRGB colour space with 2.2 gamma transform at the end? Can't for the life of me work out how to do this in AE now, it doesn't seem possible to turn off colour managment.