Hey Doug, thanks for the quick reply! 
It's definitely not a high dollar project 🙂 But… I'm glad to know that my main concern, if need be to mix with headphones, ought to come out of the eventide, rather than the iMac.
I currently have a blue baby bottle mic running thru a presonus tubepre… not the highest end stuff… definitely aware that a vocalist may want a separate mix than me, but that's easy to monitor within Logic's mixer… however, I could just send that mix to the vocalist in his/her set of decent (but not high end) headphones and get away with using the iMac's output… The question is how to hook up at least my pair to the Eventide… I can see 2 possible scenarios… maybe you could enlighten me to the best choice:
1) I plug my headphones into the Eventide's outputs (which would require a female 1/4 inch -to- dual female XLR, right?), leaving the vocalists headphones plugged into the iMac
OR
2) I pick up a headphone monitoring system (like the presonus HP4, which is plugged into the Eventide with the same adapter) and monitor both headphones through that unit.
Thoughts??? 
