If hidden you could use plywood.

Thanks! Even with a cork underlayment? Would the plywood by more water resistant -- I want to prevent future damage if the same problem were to happen -- than the plank? Would there be any effect on sound dampening to the downstairs? Would plywood or the wood planks be more resistent to the weather changes in Chicago with the dry winters and humid summers? Thanks, again!

" Would the plywood by more water resistant -- I want to prevent future damage if the same problem were to happen -- than the plank? "

No. I would remove the cork underlayment though unless your sure it is dry and still sound.

" Would there be any effect on sound dampening to the downstairs? "

Who knows for sure but I would imagine it would be the same especially since this would be under cabinets.

" Would plywood or the wood planks be more resistent to the weather changes in Chicago with the dry winters and humid summers? "

Plywood is always more stable but in small pieces I doubt it would make a bit of difference.

Wow! Thanks for the detailed response!

I used wood look porcelain tile under my refrigerator run (with water supply), and I’ll use the same under my sink and dishwasher. The cement board underlayment, mortar, and tile thickness made this the same height as my hardwood floors for a seamless installation.

The same wood and finished to match the rest nothing i water proof a flood ruins every floor the stuff under tile needs to be replaced too . Cement board is not waterproof

Thank you for all the responses! I'm going to go with the original white oak plank. This was a custom home, and insurance is covering it. Though it will take a little longer, it won't be that much longer.