Box more techy...
After guiding on the box and racecourse for a couple seasons, I can tell you the box is a level up in terms technical boating. But, there is good warm up. The rapids become increasingly more difficult as you go downstream.
CFS-wise- I've run it as low as 600 in 12'ers and as high as 8K back in the mid 90s. Anything above 1k is good.
Boat-wise, I've rowed my 16'cat down there, paddle boated 16' avons years ago when it was running 8k, but generally, a boat around 14' is a nice size on that run-either paddle or oar.
Pick up a guide for the box and study it. You'll want to scout dead car and powerline-mainly cause they're steep and quick.
The rio bravo section at the end-depends- at higher flows-about 2000? some of the stuff in there runs together and you need to be pretty on your moves in a raft/cat. Flows in the teens, the holes are chunky but reading and running is more manageable.
After that stretch, the last rapid is sunset- steep and short- I'd take a look.
The box is a great run, but you need to be prepared. Be sure to have some rope and a wrap kit-and know how to use it.