The standard way to deal with a non-symmetrical room with large openings and less than ideal placement and whatnot is to use speakers that are a bit more directional. If you use speakers that have very wide dispersion, you're going to get a lot of unpredictable and uneven reflections since one side has a wall, the other doesn't, and the placement of everything isn't quite in the "ideal" spots.
One potentially good option - especially since you desire on-wall speakers - would be the
GoldenEar SuperSat speakers . Given that you are planning to use a 70" Sharp, I'm assuming the room is fairly large and you will be sitting fairly far away, so the larger SuperSat 50 and SuperSat 50C Center would likely be the best option, since you'll need louder output capabilities if you are sitting farther away or in a larger room. The folded ribbon tweeter in the GoldenEar SuperSat speakers, I've found, tends to work quite well in less-than-ideal placement scenarios. It "beams" a little bit, which isn't always ideal, but in a situation like yours, it's exactly what you're after! You want to control the dispersion and have more of the direct sound coming at you vs. reflected sound. So the SuperSats with that folded ribbon tweeter are a very good option, IMO. You can wall-mount them. They look pretty sleek and won't be distracting in terms of looks. But most importantly, I think they'll deliver good sound quality for you, despite the compromised room and placement
Your main issue though is going to be bass. A wide open room like yours is a real challenge. A subwoofer does not "know" that only a certain portion of your house or room is considered the "theater area". Sound waves will travel where ever they CAN travel. So having a wide open side that also joins a second floor beneath is a huge challenge for the bass. For one thing, any subwoofer is going to be trying to pressurize the entire volume of air. Not just the "theater area". Any air that CAN move? The subwoofer is going to be trying to move it. Which means the active volume of air is HUGE in your case, and an extreme challenge for any subwoofer to pressurize.
The other big problem is that I doubt you want the entire house being subjected to loud, thumping bass! Again, bass is never going to be "contained" in just the "theater area". Wide open access to the rest of the house means the bass is going to travel anywhere and everywhere.
So just in terms of bass sound, you're likely to be best served by positioning your subwoofer close to your seat in the theater/games room. Allow the direct soundwaves coming from the sub to go right into your seat and that will help. Honestly, I wouldn't even try to pressurize the entire volume of air. It's just too much and you don't want to pressurize the air outside of your "theater area" anyway! So I'd opt for a high quality, front-mounted, front-ported sub with very good self-protection circuits so that you can aim it right at your seat, have it positioned close to your seat, and crank it as loud as you please without worrying that it will ever bottom out, distort or cause any sort of problems.
With a close placement and a large room, plus that wide open space on one side, I'd probably split the difference and go for something like an SVSound PB12-Plus. If the room were closed in by 4 walls and a door - again, I'm making some guesses as to the size of the "theater area" based on your plan for a 70" screen - the PB12-Plus would likely be the correct choice in terms of output for that room size anyway. By having it positioned close to your seat, you're not going to require all of its very capable output, but at the same time, you still want to be able to fill the entire "theater area" with loud, deep, satisfying bass. Then, if and when the subwoofer is attempting to pressurize the entire open volume of air with that wide open side wall, you don't have to worry about the PB12-Plus over-driving itself or distorting. SVSound's newest "Sledge" amplifiers offer superb protection for the subwoofer and simply do not allow it to distort or play louder than what is safe for the subwoofer. So can rest easy knowing that you can crank it as loud as you want and you'll never damage the sub or even get it to sound bad
So that'd be my recommendation. It should fit within your budget. The other thing you could do if you want more tactile impact than your subwoofer can produce is you could opt to install tactile transducers in your seat. These take the subwoofer output signal (they share it with your subwoofer via a splitter or using the second subwoofer output on your receiver if your receiver offers dual subwoofer output plugs) and they turn that signal into movement rather than sound. I tend to prefer The ButtKicker brand tactile transducers, which are literally a heavy piston suspended in a magnetic field. They can really shake any chair, but with a great level of detail and control so that you really feel not just shaking, but subtle differences between each bass note!
Hope that helps
