I bought four of the Great Heils from ESS when they had their sale for $140 each. I played around with them on top of my Altec A700 828 cabinets equipped with Altec GPA 416-8C drivers. I tried the Heils stacked, both straight up and one laying on it's side. Then putting them side by side, but one straight up and laid the other on it's side. With them side by side and one laid down on it's side, I tried the laid down one on the outside then on the inside. And then I tried both on their sides, side by side. Finally I have settled with them on their sides, side by side with the outside ones straight forward and the inside ones about 30 degrees angled in. It gave the blend I wanted without the directional properties horizontally. Because on their sides they have good vertical dispersion but not good horizontal dispersion. My room is small and I just didn't like them straight up like they were designed. I also tried tweeters but took them back out as they weren't needed as far as i am concerned. Look up the ESS AMT6 to see how ESS designed the AMT6. Maybe if I could get them more at ear lever I would like them stacked straight up.
I used REW and set the miniDSP parametric EQ. I still had to tweak the miniDSP to lower the Altec horn and Heils as both were too loud or hot. Added delay to the Heils and it is sounding good. I crossed over the Altec's at 1150hz 6db and the Heil's at 2000hz at 6db which gave a -4 db at 1514hz. I tried all kinds of crossover combinations from 500hz to 2000hz 48db, 24 db, 18db, 12db and have settled on the 6 db.
My next thing to do is roll out the Altec's and roll in four Peavey FH-1's, two per side with Eminence drivers and see how that sounds with the Heils.
I did put my horns back on top of the Altec's and took the Heil's out but that didn't last long before I went back to the Heils.