DUNLAVY SC-VI

The SC6 was intended for rooms no smaller than 20' x 30'.
The size of the speaker (mostly the woofers) are there to be able to reasonably and accurately fill a space this big.
If you try to fit them into smaller spaces you not only run out of room to be able to properly adjust them but you end up having to listen at less than ideal volumes so as not to overload the room with bass.

That being said, if you were to use them you would want to put them at the shallow end with regards to the ceiling. Assuming exact dimensions stated for the ceiling would put the back of the speakers no closer than 3.5ft to the back wall. This puts the baffle a little over 6ft. from the back wall. And assuming an exact listening distance of 10ft. leaves you with just about 4ft. from the listening position to the back wall. All in all, these are not bad dimensions to work with. The distance behind the speakers should give you a nice deep soundstage. And the four feet behind the listening position will alleviate a good amount of that reflected distortion.
Having the ceiling slope upwards as you go towards the listening position will shift the ceilings first reflection higher and pretty much send it overhead of the listening height. Therefor, the first place you want to add room treatment is on the wall behind the listening position and have it extend to at least 8ft. high.
Some diffraction treatment on both side wall first reflections would be the next priority.

You wont have any room left over to control the bass but this setting should work out pretty well for the rest of the spectrum.

In the manual for the SC-III, Dunlavy recommends sitting about a foot from the back wall and treating the back wall with 4" thick acoustic foam (four 4'x2'x4" panels would probably do it). Or at least that's the recommendation for a room about 20x13 in size, where a 10' listening distance would put you near the back wall. (I still have my SC-IIIs and wish I had a room this size to stick them in.) It would be interesting to see what the manual for the SC-VI recommends.

@ Daverz, you are correct in linking that recommendation with the room size.
Dunlavy made seating recommendations based on a list of priorities.
The first was to always use the long wall if possible. This was to first increase the space between speakers but, just as importantly, to increase the relative distance of the direct sound versus the first reflected sound from the side walls.

The second priority was to keep the speakers off the wall behind them as much as possible. This also was to keep the difference in timing between direct sound and reflected sound relatively high. It also helps to increase sound depth.

Of course, all Dunlavy speakers were designed for a 10 ft. listening distance. So the distance from the listener to the wall behind him/her was the last priority. And in normal size listening rooms usually meant the listener was right on the wall. In this case, the easy fix is to cover the area with thick absorptive material. Leaving this wall for the primary wall treatment also meant that you could get away with a lot less material since the closer you sit to the wall the smaller the area of treatment necessary.

Given these priorities it is easy to see how the size of the room will ultimately impact the placement recommendations. Hope that helps!

A lot to consider. The room is being made out of an existing structure which is empty and stripped to open wall studs and open ceiling joists. The slab it sits on is within inches of 20 x 20. If I keep it 20 x 20 then I do not have to do any new roofing, supporting walls, etc.
Putting the speakers on the short wall makes sense to me acoustically since it makes the room more "amphitheater" like.
Kind of like a horn. The only deal, is that I wanted to also add a Runco and 120" screen for a... dare I say it... um... home theater... the 9 foot high wall would be ideal for a sreeen.... perhaps I could do an automatic drop down screen a little off the short wall, so I do not have to try to mount it on a 6 foot wall...

Not a bad idea putting the screen as a drop down.
If I were you I'd invest in a good acoustically transparent screen (so as not to cause adverse reflections from speakers) and hang it so that it's approximately even with the baffle of the speakers. If you use the short wall side this will put it out about 6ft. which will also raise it by ~1ft. which should be plenty high.

It all sounds interesting. Keep us posted!