Recording multiple MIDI tracks in Cubase LE

[sir]

hi everyone.
I have cubase LE running here with my Yamaha S90es synth. I made two MIDI tracks, and recorded a fairly simple melody on that track. Next, i selected the second MIDI track and tried to record a beat to go with the first track. However, when I tried to play back the first track, it played it back through the synth and came out in the drum voice that the synth was set on... so i can't do both lines simultaniously.

i have tried to figure this out for like, 2 days so i decided to join a forum and get an answer, since i couldn't find it anywhere. Hopefully it is a simple problem and really easy to fix... so if anyone can suggest what I might be doing wrong, that would be awesome.

And please be as clear as possible, I am pretty new with all of this home recording stuff so I may not understand everything

Thanks for any advice