Being that you have the MIDI device set up in the External Devices list and you are receiving MIDI data in the MIDI Monitor, it appears that your device has been configured correctly. You may want to double-check that you set the device up as a new keyboard and not an instrument. If you check the box to set the instrument as your default, it should always be selected for input, regardless of the virtual instrument that you load. If you need to manually select your input device, you will want to open the Inspector window for the track that you are working on and verify that the input is set to the desired MIDI device. If you take a look at the MIDI monitor, you should be able to identify which pad is sending which note on signal. You can then verify that that note-on correlates to a sample in Presence. If you are using the "Prime" version of Studio One 3, you do not have "Impact" which was designed to work with drums. Here is a comparison page that shows what is included in each version:
https://www.presonus.com/products/Studio-One/compare-versions