Welcome!
Quite the large room you have there! And a nice budget for speakers.
Certainly, your biggest challenge is going to be the bass. Your subwoofers will not "know" that the designated "theater area" is only 19' x 15'. They will simply try to pressurize the entire space. Where ever air can move, the subwoofer has to move the air.
So this is a massive space - over 10,000 cubic feet - perhaps quite a lot more depending on your ceiling height.
The question is - do you want the sound to fill the entire space? Or do you have it in mind to try and somewhat "contain" the sound to the "theater area"? It's all well and good to get you some massively powerful subwoofers that can fill the entire space, but if you really do not want that, then we're working against ourselves, aren't we? If you're only concerned with having sound within that designated "theater area", you might very well be better off using a split bass system, with a mid-bass module placed close to your seat so that you get all of the tactile impact from the 40-60Hz bass where the "gut punch" bass lives without needing insane output levels. The lowest octave will still require massive output if you really want to feel all the "tingles" and the "eye shaking" bass trembles that the lowest octave delivers. But if you keep those subs to the closest corners, you should be able to get the output you're after.
With the speakers, it's more about your seating distance. They do not need to "fill" the entire room the way the deep bass subwoofer does. They merely need to be able to deliver the volume level you desire at your seat.
You said the room would be open behind you. So I take it the plan is to set up the display on the 19' wall, have the seating around 15' from that wall and then have the remaining 45' of the room behind the seat?
If I am correct about that setup, then you do need some speakers that are capable of high output. The whole "towers or bookshelf speakers" thing is immaterial, IMO. My stance is that the bass should ALWAYS be handled by subwoofers, since placement and room interaction is so vitally important when it comes to bass. Using "full range" speakers makes no sense to me since you are now totally limited in the placement of the bass transducers to where the speakers need to be placed for proper imaging and soundstage.
So I don't go for tower speakers that use their extra size and number of drivers to play lower. Rather, I would go for larger speakers that use their size to play louder. Forget playing lower. Let the subwoofers handle that. Just worry about playing louder and playing low enough to properly cross-over with the subwoofers.
For surrounds, I would not recommend di or bi-pole surrounds in a space like that. Part of the idea with a di or bi-pole surround is to reflect sound off of the back wall in order to create a greater sense of envelopment and a "wrap around" effect. Soncially, you essentially have no back wall, so a di or bi-pole surround speakers serves very little purpose in a case like yours. Rather, I would recommend that you use a 7 speaker setup. Surround back speakers make perfect sense in a setup like yours in order to "fill in" the "hole" in the back of your surround field. So long as you have the surround and surround back speakers placed 3 feet or more above your seated height, your room size will take care of the ambience. you don't need to "trick" your ears into hearing "more" speakers with di or bi-poles in your case. You can use in-ceiling speakers or ceiling brackets if you have no where to mount your surround and surround back speakers. Their job isn't to create pin-point perfect sounds. It's to create ambience and envelopment, so there's nothing wrong with using in-ceiling speakers for the surround and surround back positions, IMO.
So, there are a few ways you can go in order to get the kind of output you will need from your front speakers. You can go with horn-loaded speakers. You can go with a line array, or multiple drivers for each portion of the frequency range, or you can go with brute force.
If you really want to "contain" the sound to the "theater area", then a line array is your best bet. Line arrays are extremely directional. You can essentailly "aim" the sound at a specific spot. The problem is that it really is only best suited to one "sweet spot" and it can sound "in your head", rather like you are wearing headphones rather than listening to speakers.
Horn-loaded speakers can also be more directional, but this is the most efficient way to get higher output. All of the speakers you'd find behind the screen in a commercial movie theater are horn-loaded. Almost all concert speakers are horn-loaded, unless they are line arrays mounted up high and aimed downward at the crowd.
The brute force approach of simply using very strong drivers that can move a great distance and absorb a TON of power is how you get "room filling" sound that will spread out and cover the entire open space.
The speakers that immediately jump to mind in a case like this are the RBH T-1 speakers. They use multiple high output drivers, but not a full line array. What could work quite well for you would be to actually use the "T-2" setup where a pair of twin 10" (four 10" drivers in total) subs are used as "stands" to make the T-1 speakers look like very large towers. You could have those up front, and then have two speakers mirror the placement behind your seats to essentially give you 4 subwoofers in an arrangement that should give you very even bass response at all of your seats as well as very good "smoothing" of any large peaks or dips in the bass response.
So I'd recommend a pair of RBH T-2 front speakers running full range, a matching T-1 center, a pair of SVSound PB13-Ultra subs behind your seats mirroring the placement of the T-2 towers up front, and some RBH in-ceiling speakers for the surround and surround back positions.
