Maybe I'm confused - are they piping in the track and they want you to play something over it? Or do they want you guys to come up with a musical accompaniment based on that track? Like @mambo4 said, there's already a bass line there - mostly a lot of whole notes on synth, but it's in the bass register. If the track is playing and they want more, I'd say go high and melodic. If it's just you, then you need those roots in the music, and I would focus on touches to add some flair rather than just hanging the whole notes out.