Speaker placement for 2-ch AND 5-ch same room

I am building a dedicated room for my gear. I have reasonable architectural freedom, but not unlimited space. Right now we're looking at 15 x 21 x 9 or thereabouts.

I have suddenly realized that I have enough equipment to install two separate systems, one for 5-ch and one for 2-ch. I'm looking for advise as to how to position the speakers. The 2-ch mains are MartinLogan Odysseys; if we go with two systems, the 5-ch mains would be ML Scenarios with Cinema center. The screen is retractable and automated, so I could have the screen drop in front of the Odysseys and place the Scenarios outside of them and slightly in front. I think that putting the big Odysseys outside the Scenarios would start to put them too close to the sides of the room (screen is 92" diag = 7' 6" wide plus tensioning).

My priorities is 2-channel, but I got WAF by making the 5-ch movies work well.

Any other suggestions? Am I nuts?
Wow! You increased the WAF by using 7 speakers.

Actually, the set-up you suggest sounds reasonable so long as there is nothing between the Odysseys (e.g., gear racks) and they are still away from the walls, and it sounds like they are. The soundstage may suffer a bit from having another set of speakers so close in, but you can check the effects of this by simply moving the Scenario's away (e.g., 5 feet or so) and see if there is any noticeable difference while listening to the Odysseys. If the speakers sound much better to you without the Scenario's nearby, consider having some easy way to move the Scenario's back and forth as needed for movies.

My first thought was that you should simply try HT on a stereo setup, but that big screen would force you to move the Odysseys only about 3 feet from the wall. That could also damage the soundstage and imaging. But, sometimes it doesn't seem to matter much and you might also want to experiement with that. If the Odysseys sound just fine in a position that allows you to utililize your screen without moving the speakers, you might want to sell the Scenarios and buy your wife a nice gift (hey, maybe there'll be something left over for that upgrade you've always wanted). You could still use the center and rears with the Odysseys, but you may also get away with just using a pure stereo mode. Experiment and trust your ears.
The screen is retractable, which helps a lot.

I was trying to figure out how to get the 2-ch and 5-ch together in one - in fact, that was my original intent. But tube gear generally is not good with remote controls, and useability of the 5-ch stuff is CRUCIAL as my wife is simply not going to fiddle with more than one remote. In fact, at the moment there are three buttons to push and this is nearly ruining it! If I separate things, then I have an easy-to-use solid state system for movies and an old, muzzle-loading analog tube system for music. The common components are the room and the subwoofer. I was astonished to find that the Descent has provisions for this sort of thing!

Anyway, I'm asking now because the room isn't built yet and I'm more than a little suspicious that my current temporary room won't let me evaluate this. (It's 13x14x7 - can you imagine that with 7 speakers in it? Especially with the Odysseys 4+ feet from the 14' wall?!?!) I should post a picture of it - it's a riot, but all I have until the addition gets built.
"Necessity is the mother of invention" and "Where there is a will, there is a way" come to mind. With 7 speakers in the present room---I'm betting you'll be going for 9 in the larger room.PS, don't forget that extra center for the rear;for "pro-logic-2".
Here is some food for thought,before speaker placement issues,note that your dimension of 15x21x9 have a commom denominator of 3,meaning all dimensions are divisable by 3.When this occurs(all dimension having the same common denominator) there is a chance of peaks(boosts) and vallies(suckouts)at certain frequencies do to the room dimension excessively renforcing each other.Is it possible to stretch the room to 16x23x9 ? I would contact Audiogon member RIVES,and run it by him.I may be overracting,but an ounce of pervantion is worth a pound of cure.
Good Luck

Blw, with the "remote" constraints, I can only say that you have done a masterful job managing the situation. You still may wish to experiment with moving the HT front speakers later (i.e., away from the main speakers when playing music and then back again for HT -- see if it matters and find a simple, wheeled?, way to do this if it does), but apart from that, it sounds like you are far from nuts.
Davehrab is correct. Dimensions which are exact mutliples do tend to reinforce or boost the same frequencies and create dips in some others -- in a 9x15x21 room, those boosted frequencies are at 188 Hz and 377 Hz with some fairly big gaps or dips in the ranges of 81-107, 161-188, 188-215 and 269-296. If the dimensions are off a bit (e.g., 8'9" rather than 9'), it will affect these in a relatively positive way. My understanding is that anything above about 300 Hz is not a big deal so the only real peak is at 188 Hz and that could be managed with specialized treatments. The 27 Hz gaps might be a bit of a stickier problem. Rives knows more about this and will undoubtedly have more to add. Feel free to ask questions though and I'll give it a shot as will other more learned Audiogoners. Good catch Dave.
Haven't been to Rives' site yet (travelling this week, really busy) but I'll do that. Dropping the ceiling 3" would be no problem whatever - we'll just dig 3" less.

Where is there reading material about this? I know about the stuff at Cardas and the much more general stuff by Robert Harley. I'll definitely dig into the room sizing thing.

Anything else on speaker placement of those five front speakers (2 L, 2R, 1C)?
Try the book Sound Studio Construction on a Budget by F. Alton Everest. Good stuff. BTW, don't drop your ceiling yet, I was talking in generalities. I'll be happy to send you a spreadsheet on these calculations so you can test different dimensional impacts. Let me know if you are spreadsheet savvy and I'll work on it over the weekend to make it a bit less subjective and easier to use. Cheers.
If you're really looking for world class performance from your system, as you're obviously ready to plunk down sizeable cash for your gear(which is not even half the battle really), may I highly suggest having a professinal work all that out for you!!! There's simply far too many variables to consider, and too many factors that are involved in achieving a perfect balance between flat/even frequency response and the best anchor spots for all the speakers, from all the pertinent seating possitions. There's another long long list of variables to consider if one wishes to "do it right" as well...but that's getting off track here.
A quick answer for you is that you might try going back through all the past Stereophile Guide to Home Theater mags for the past 3 years or so, and find Russ Herschelmann's "Home Theater Architect" on going article, and read all of em!!! Other recommended reading is the stand-by, F. Alton Everest's "Master Handbook of Acoustics"
Also, you could check any other HT and Audio Mag for back articles on acoustics, room set up, bass vs. Space, speaker/seating suggestions, etc.
Anyway, I personally would need to see more of the particual room to make some more "hard" suggestions, calculations, and recommendations myself. Also, how flexible you are with seating and/speaker locations and layout will make a huge differnce as to the potential of the project, and what kind, if any, of a level of "EQ'ing would be needed for the HT system(yes, the dreadded Audiophile "bad word"...EQ).
This all may or may not be as much as you want to hear from your inquirey, but it's the truth.
Yes, you're on the right track with getting assistance to proper speaker(and seating) location for best sound, but it's just not that simple, to say "put them there or there, etc"...that from years of experience of doing 100's even 1000+ set-up's! There's a lot of fine tunning, trial and error, and knowledge that goes along with getting world class sonics out of any room/system!...make no mistake about it.
Anyway quick answers to your question really It isn't that simple to be true.
People Like R. Rives @ Rivesaudio.com have a website you can check out for some consulting ref's...might check them out. Also, if you're looking for a cheaper route than "Consultants", may I suggest attending one of Russ Herschelmann's anual seminars in San Francisco! Russ is probably the premier custom theater deisgner/acoustical engineer/consultant in the biz today, has worked on the largest jobs(including the I-Max at Disney World), and writes for Stereophile GHT, HT Mag, and AV Interiors on acoutics and HT related...definetly worth the $1000 or so to attend his work shop!
So be informed however, that simply reading it all won't replace experience, which you cannot expect to replace with some "head Knowledge"...cause there's no replacemnt for years of tried and true eperience and skill!

P.S., give some more details of your room/structure/possible obstacles and I can give some more solid suggestions