https://docs.google.com/spreadsheets/d/1ZsJkCX4DIv2oeCKQ7zp2ArkR1qKEXCUuCMBbUtHtmh4/htmlview
Sounds like you're asking specific to iTunes, so below is ATV4k-centric.
Fox - you have to redeem iTunes from foxredeem to get 4k on ATV4k. Codes don't need to be from 4k disc.
Universal - redeem directly on iTunes. Codes don't need to be from 4k disc.
Paramount - redeem directly on iTunes. Codes don't need to be from 4k disc.
Lionsgate - redeem directly on iTunes. Codes don't need to be from 4k disc.
Sony - from 4k disc, code needs to be redeemed on MA to get 4k on ATV4k (no UV rights); if you redeem at Sony, you're locked to Sony Ultra for 4k, but you do get UV rights
WB - from 4k disc, code needs to be redeemed on Vudu. This will get you 4k on Vudu and iTunes, as long as you're linked on MA