After reading the EasyAPI documentation, it appears that using an REU and EasyFlash at the same time is out of the question due to a conflict of the REU residing at $DF00 and the EF placing RAM at $DF00 to $DFFF.
If this is indeed the case, are there plans to create a version of EF in the future that would incorporate a 17xx compatible REU in the EF cart so that software can target the EF but also use the REU for large buffers?