Since Whatbox allows you to SSH into your seedbox, you can setup slskd manually (root not required) and access its WebUI remotely.

This tutorial is pretty good as an introduction to modding APKs:
https://old.reddit.com/r/ApksApps/comments/oat3qu/tutorial_how_to_modify_apk_files_for_premium/
The example used is unlocking premium features but the principles are the same for disabling DRM.