I managed to find a thread that has amassed a list of rewards and the criteria required for each one based on what the voice commends you for.
- Completion of Machine Lifeform Quests: Heal Drops Up +6
- Frequent Hacking of Machine Lifeforms: Hijack Boost +6
- Completion of Android Requests: EXP +6
- Collection of items (Dropped?): Drop Rate Up +6
- Recover a lot of bodies: Max HP +6
- Kill a large sum of machines: Faith
- Use a large sum of items: Full Restore
- Literally drop dead a lot: Reset +6 (I think it has to be over a hundred deaths. I got it my
first playthrough but not my second at 66 deaths)
It may depend on your playstyle and overall goals, but the most important reward is the Faith weapon, as there are trophies and an ending related to collecting all weapons (not to mention the chips given do not have diamonds and thus, have very high memory costs and could be fused on your own for less). Both times I've gone through this part, I've received the reward for machines killed, so it seems virtually unmissable. If you are attempting to collect all of the weapons, you don't need to worry about not killing enough machine lifeforms.
It's also worth mentioning that even if you miss out on some of the chests the first time you do this in your file, you can always use chapter select to go back to this point. Any chests you didn't have available the first time that you've met the criteria for since will be made available to you if you return to the Soul Box via chapter select.