The boops only play in the game and not in Sappy because Sappy's emulation of the sound engine doesn't play anything for drum notes that have no samples. Go to "edit voice table" and go to instrument №125, which is your drums, and click the "Edit..." button to edit the drum part's sample list. This will open another, different voice table whose samples correspond to each drum note. Because the notes which lack samples are set to hardware square waves by default, they will make boops.
Assuming you're using Anvil Studio, to find the number of a note, right click on it and click "properties" to bring up the note properties window. Anvil has an annoying habit of numbering from 1—128 instead of the usual 0—127, so make sure to subtract 1 if the list begins with 1 rather than 0.
At this point, you just need to change the "output device" to DirectSound and give it a sample address. What I like to do with drums is take the addresses of samples from other drum instruments (№124 and №127 are the most complete) and compile them into one complete drum instrument so I'll never run into boops later. The most common samples to be missing are alternates, e.g. acoustic and electric snares, highhat 2, crash2, ride2, as well as several of the toms (low, low floor, and high mid are usually already okay).