You seemed to say that you could sequence the other 7 sounds correctly. If so, make sure that you are sending the correct MIDI note for the kick drum. You may have inadvertently caused the DRM to learn a non-default note number for the kick drum. If in doubt, reset the MIDI assignment for the DRM1’s sounds using the procedure given in the manual.
None of this has anything to do with MIDI CC messages.
Yes. Each MIDI sequencer track on the Octatrack is capable of sending different notes, as many as four on each MIDI sequencer step. See pages 113 and 114 of the OT manual. You will have to calculate the note offset value from the default note value in order to get simultaneous drum sounds, so it is a little bit awkward and you may prefer to use more than one MIDI sequencer track for convenience.
You did not include a video in your post.