Hi and welcome, Mark.
Are you trying to play OPB songs from the BeatBuddy (BB) and if so, does it happen with all drum sets or just certain ones? Some kits have the drums panned to one side and the bass panned to the other.
Hope this makes sense. Are you running a stereo patch cable from the BB headphones output to the Spark aux input? If the amp aux input expects mono or stereo patch cables, this could be why the drums are not sounding thru your amp. I reviewed the Spark amp specs and could not tell if the aux input expects mono or stereo input—I think it would be stereo. If you’re using a stereo patch cable from the BB and the Spark aux input expects use of a mono patch cable that could also be a possible cause.
A simple method to rule out the BB as the source of the problem is to to plug a pair of stereo headphones into the 1/8" headphones output and play the or beat that the drums don’t sound. This might at least narrow down the source to either the patch cable or the amp aux input.
Let us know what you had to do to get it working.