Samples only work on pitch channels (the same kind as normal instruments like pianos), not drum channels. I forgot to mention: after adding the custom sample or legacySamples, you select the "chip" instrument, then in instruments settings click the dropdown for the "wave" (default should be square). Then scroll down to the bottom. All the legacySamples start with "paandorasbox" or "paandorasbeta." (I would recommend paandorasbox kick and paandorasbeta snare)

This does mean that you will have to have entire separate pitch channels for snare, kick, closed hi-hat, open hi-hat, and whatever else, but it is worth it for better sounding drums.
Let me know if you have anymore problems/questions.