Hi phoenixrae,
Glad you liked the article. I should go back and update it where required. Pmbuko nicely covered the cosmetic/practical issues of vertical or horizontal placement of the EP600.
As to the effectiveness of vertical vs. horizontal placement of the EP600, in theory it shouldn't make any significant difference in pressurizing the room. That said, no room is identical and you may find you hear a difference with vertical vs. horizontal placement.
As to your proposed selection, I'd kinda like you to choose the M80s over the M60s, mainly because your room is really large and the M80s are just a teensy-weensy bit smoother through the midrange than the M60s, especially on vocals. We are talking tiny nuances that are only audible on immediate double-blind A/B comparisons, but since I just spent a week doing those at the Axiom plant, I can tell you that with confidence. The M80's dynamic capabilities at loud playback levels will also better match those of the EP600.
Either way, you're going to a have a dynamite system.
