Soooo, the short version is if you want Grade E air, then you really need a compressor/filter stack assembly that's designed as a whole to produce that grade.
Nonsense. Grade E is ridiculously easy to attain and is pretty much done with stock filters that come with the compressor.
Most compressors that meet Grade E also meet the pseudo-standards of ANDI's O.C.A. and the NAUI's "oxygen clean".