I've never felt a need for an in-between grit, between the DMT EF (9µ) and the EEF (3µ). I've always been impressed at how efficient DMT's 3µ products are (both hones and strop paste) at very quickly cleaning up & refining the scratch pattern coming directly off the EF hone. In fact, in using DMT's Dia-Pastes, I've also seen little need to use the EEF hone (3µ), before stropping with the 3µ Dia-Paste, as it raises a high-mirror polish on it's own, right off the EF DMT hone. Important to note, I do this polishing on smooth & firm wood, like basswood.
Some have commented that the EEF (3µ) hone takes too much 'tooth' out of the edge, in finishing on that hone. It's more a polishing hone, in terms of edge finish. I could conceive, if one were looking for an alternative to the EEF for a little more 'bite', then the 6µ hone might be worth looking into for it's own finishing characteristic, which might (but I don't know) retain a little bit of tooth in the finish. But I don't see it being necessary as an intermediate step between the EF and EEF.