The IMAX equipment (speakers, amps, projection screen, projection system, etc.) all comes from IMAX and is the same gear, same engineers, same support chain as used in the commercial IMAX theaters. An IMAX private theater will never be a DIY project. While IMAX does not do the construction of the room the fundamental system engineering (acoustics, seating placement, etc.) is all done by IMAX engineers.
In much the same manner, a THX Certified Professional Screening room, is engineered by THX, you use the equipment they suggest for the room and all speaker placements, seating placements, etc. are designed or approved by them (and subsequently they come in and validate and test the Audio and Video to make certain all the specs align with their requirements.
In other words, for both THX and IMAX, if it ain't their stuff, ain't their engineering, and doesn't meet their specifications when completed it ain't IMAX or THX. End of discussion. If you want to build your own Ferrari in your garage, have at it; but, what rolls out will not be a Ferrari.