I noticed the recipe for sand is craftable in both the assembling machine and the K2 Crusher, but the Crusher will not accept stone as an input. Am I missing something? I'm just hoping I don't need to resort to the massive assembler chain for all my sand.

Thank you for making the pack, it's been fun so far!

Hmmm... I don't have such problems. The K2 crusher doesn't have recipes; instead, it destroys everything it puts in, even if it doesn't have a recipe.

Further testing shows it takes all inserters except the throwing variants; immersite and immersite crystal; biter, pentapod, and wasp eggs; but not stone. It gives me a "Stone cannot be smelted" error when I try and place a stack into the input. If it helps, the part that lists mod adjustments shows:
Krastorio 2 Spaced Out > Cargo Crates
Krastorio 2 Spaced Out > Machine Upgrades > AAI Industry > PlanetsLib > Maraxsis > Cerys > Panglia > Cargo Crates > Planet Pelagos

In the factoriopedia, it does show stone to sand as a valid recipe alson with the tested ones above.

Any suggestions I can try to find the issue?

I think I found the culprit, it seems if the optional dependency AAI Industry is enabled the stone recipe is broken. I can't seem to find any other mention of K2 and AAI Industry having this issue, but I'll keep looking.

It's the null's mod fault. There's already a report about this.
https://mods.factorio.com/mod/nulls-k2so-tweaks/discussion/69e79d2a419251f36c2a5aa2

Thank you, I didn't think to check anything that was not in the chain listed in the item properties.