Nice looking room and congratulations on getting so much in there and organized well.
Based on your pictures I’m sure you won’t get much benefit from height speakers. While it’s going to be tight I still think you would most benefit from using wide speakers but looking at your pictures it might be a closer call as to which works better for you, wide or rear speakers. I have a feeling the only way you are going to know for sure is to try it out.
As a test if the wires are long enough I would move the rear speakers to the sides of your main seat on either wall even with or a little behind the main seat if the door isn’t in the way and aim them about at the table in the center of the room. Then move the side speakers forward to about where the front of each side couch is and aim each one at the closest side of the main seat. Then reconnect them to the appropriate outputs on the receiver and play with the positioning to see how you can get it to sound.
I still think you would benefit by trading up or buying QS speakers to use as surrounds. The reason I mention buying is that some day you will likely end up with a 9.2 or 11.2 capable receiver and from looking at your room I think you would get even better results using both wide and rear speakers. I’m not a big fan of rear speakers except in certain situations and with how spread out your seating is I think they would allow you to get better 360 degree surround sound especially for your side couches by using wide, surround and rear speakers.
Actually if you just move our M3s around you may find you like the improvement enough to put off even getting QS speakers for now and just enjoy what you have until you do eventually have to get a new receiver again.
As for the subwoofers I would go with HSU. Emotiva subs are to new and have no independent reviews or measurements that I know of. As for ED I’ve recently read a couple of threads over at AVS where people have had issues with ED quality control and then customer service when trying to get things fixed, here’s one of them. http://www.avsforum.com/avs-vb/showthread.php?t=1242263
I realize that all companies will have their complainers but it’s just something to consider especially if you have to deal with warranty issues from Mexico. Also I saw your subwoofer thread over at AVS and was wondering if you found any of those subwoofer manufactures had local dealers to ease the cross border shipping hassles?