While I think an integrated would be a good choice to develop a collaboration, here are a few roadblocks to your requests:
1) THX uses class AB with low A bias, to my knowledge there is no class D in play for their tech. And personally I wouldn't want it to be, never found a class D amp in the same price class that competed with AB offerings. Hybrid "H" designs are a better option IMO than full class D.
2) Even if the first pre-order had already completed the chances of getting it out by Christmas would be almost non-existent.
3) Squeezing an integrated with that much power and those connections into the case of a 789 is borderline physically impossible, smaller is a pipe dream.
4) Pricing could be difficult, the only THX speaker amp is the AHB2 from Benchmark at $3000 but that is based on the 888 module and not the 788 module.
Not trying to rain on your parade here, just bringing some issues with getting all of that in the form factor you are looking for. If you really need something that small to run a passive system you may be better off looking at the Parasound Z series. They are very small and the pre combined with the amp is running around 650-700 bucks these days and available to ship now.
Here is the interior of the AHB2, not seeing where one could fit all the preamp or DAC functionality and this is larger than the 789 case already