If you want a system that can rival an Imax, you are on the wrong track. Forget full range tower speakers, forget Aperion. I would rule out the Emotiva stuff as well. if you want an imax sound, you will need speakers with a high dynamic range and subwoofers, very good subwoofers. In your budget I would be looking at speakers like Pi Threes or Fours, JTR Noesis, JBL Pro, and so on. For subs I would be looking at Funk Audio, Seaton Sound, JTR. For electronics I would just get a good AVR, preferably one with Audyssey's Sub EQ.
Here is on system suggestion:
AVR:
Denon AVR-x4000, This receiver has Audyssey's top of the line equalization system, it will automatically calibrate the sound for you. What's extra nice is that it has Audyssey's Sub EQ, so it can independently calibrate separate subwoofers, which can save you a lot of time dialing the system in. It has pre-outs in case you ever wanted to connect the speakers to separate amps.
front stage speakers:
Pi Threes w/ upgraded woofer and tweeter. These are high sensitivity, high dynamic range speakers with
very good sound quality and an easy impedance load. Any AVR can drive them to blazing levels, and they do not need separate amps. They will be far more powerful than the Aperion speakers. THX Reference levels, here we come!
surround speakers:
JBL 8320. These are THX Certified, 8 ohm surrounds, the available measurements show good performance and they are easy to mount. They would be an easy load for any AVR, they do not need separate amps. They are inexpensive too, in fact, the least expensive THX certified speakers available, but they will still be powerful. That means a lot of bang for your buck.
Subwoofers: two passive
JTR Captivator 2400s powered by two
iNuke 6000 DSPs. Welcome to boomtown. This sub system is so far ahead of the Aperion subwoofer you were considering that they are incomparable. You would need many, many Aperion subs to equal a single Captivator with respect to performance. The iNuke amps should work well, there is the above linked DSP version lets you tweak the response and also limit the low end excursion. I would get the DSP version. In your room, Caps plus iNukes would get you huge and very clean bass which can dig to such low frequencies that it can only be felt rather than heard.
That is a $10k system more akin to what you hear at the Imax, and in a room like yours it could easily surpass Imax sound and go well beyond THX Reference levels. It will absolutely smoke a Emotiva/Aperion setup with respect to dynamic range. To address one of your questions, at your budget level, skip bipole surrounds, especially for a seven channel surround sound system. Seven channel surround allows for a more clear surround sound stage which would be wiped out by the ambiguous sound of bipoles or dipoles. Monopoles (speakers which project sound in a single direction ie conventional speakers) will give you a more articulate and precise surround sound stage.