6 across: 8, 27 and 64 die (5)
I’m calling it as DA’s second error in a calendar month! Here, 8, 27 and 64 = cubes = die, which is incorrect because die is the singular form of dice, meaning that the clue should have been 8, 27 and 64 dice.
It’s too bad, because it would have been a candidate for DA Gold otherwise (I like maths, and I have a sneaking suspicion that mathematically-minded people are the best at cryptics).
Update: This is not actually an error. AL set me on the right course.
As AL pointed out, I am in error here, not DA.
I read the clue as suggested above, 8, 27 and 64 = cubes = die, which would have been a DA error.
The alternative is to read it as 8, 27 = cubes = 64 die, which is not a DA error.