A simple overhead surround well it has to consist of many cheap bookshelf speakers for the surrounds otherwise it will surly bust the budget and the "x wife factor show" will be sharping the axe in the shed.
Overhead surrounds isn't a new invention to me. It has been done at UCI tower park 10 screen plex 25 years ago and worked fairly well with the number of films I projected or if had time nip into the auditorium or of off days pop down and pay to see a film in Dolby Stereo or SR.
The speakers where as remember where EV Electro Voice that had slanted angle on the baffle and was attached to the suspended ceiling in the various two size auditoriums small and large. Small ran though 1 to 4 and 7 to 10. Large was 5 and 6. The arrangement in the smaller screens was bit odd due to where the booth was located.
Rough layout of what UCI overhead surrounds Dolby Stereo A SR looked like, 25 years ago. Smaller screens with one door to projection booth a few steps to walk up and cake platters in the middle with Cinemeccanica Victoria 5 35mm and Dolby CP55 with SRA5 Spectral Recording.
If I was going to replicated the overhead surround like one of the larger screens 5 and 6 I think they had x6 or x8 EV on the ceiling? Its 25 years ago.
I would fit just any good cheap bookshelf to the ceiling along with same for side wall and back wall fit a few subs on the surrounds to extend the lows down further. I think my Harman Kardon AVP1a has multi outputs with sub bass surrounds, thou I use it for filtering other subs LCR extension and seat shakers at 80Hz just to cut some corners. It seems now with atmos they add in sub bass on the surrounds and I think Lexicon and Harman have already done this, yonks ago.
If I had another few matching cheap AVR with PLIIx I would splice the outputs RCA from main AVR into the side wall surrounds and of the x2 matched same AVR just use Lt/Rt input and use the PLIIx matrix decoding for cheap ebay fun of surround as the typical AVR with yesterdays with all the bells and whistles on it, can be brought for ether £150.00 or under £100.00 and use the amps on it to power the side wall and back wall and overhead surround arrays and use the crossover to feed subs though the sub RCA output to some arrays of surround subs.
If the room is large lucky for some then fit all the bookshelf into the false plasterboard (drywall) along with the smaller size subs matched or why not try car hi-fi subs and some pre-made boxes that should keep the costs down and buy some second hand amplifiers to run the subs and EQ 1/3 for each sub or if fussy use a DSP parametric type.
If you use the speaker outputs on the AVR most have auto EQ maybe who knows an Audyssey and just set the mics up and run the test for each AVR one at a time it would be tricky to set-up cos the main AVR will have ether an Audyssey and if so it would have to be switched off as any surround EQ would mess up the matrix signal on the other AVR's. Myself I rather use 1/3 its a lot faster for me to do it and check each channel/s at same time.
The surrounds (mono pole) keep them spaced apart on side wall and as shown above so the U.S.S. Enterprise on TOS STAR TREK region 1 first pressing same as region 2 DVD 5.1 whooshes along the side wall each right then to left and right and left on the opening titles. The spacing of the surrounds will have some diffusion and some location cue, without the TNG "Q".
Also a good episode
Court Martial where captain Kirk, goes looking for Finney, in the engineering room, the voice Finney, pans along each side surround and nicely fills in my reference Dolby THX cinema over wide listening area around the seating.
Another old use with matched matrix decoders is creating a 5 screen front. maybe that is better than PLIIz. I'd like to have cheap PLIIz AVR to compare with PLIIx and put each one though a close thorough scrutiny listening test.
A PLIIx AVR has 7 directional full range channels. Front LCR or LR will be used for side wall surrounds the centre can be used say a middle over or just experiment with it and watch/listen to the film closely to see where sound objects are move off too?
Use the surrounds well maybe overhead left/right and the rear surrounds left/right maybe as below seating surrounds that is what I would go for or try each surround and back surround to see what the decoder makes of it? Experimental is all it. Repeat the same idea for back wall surrounds and see how back that can be expanded?
I think some other enthusiasts have ether already given it a try?
I'd use the LCR and and LR for back wall and centre for extra centre back surround? ether placed on same wall shared between the other x2 surrounds on the wall? Experiment with it, have fun.