Yamaha DTXpress/DTXplorer/DTXtreme

I have a CD player connected to the AUX/IN in front and cassette deck
connected to the two outputs on the back side (I think they are 1/4"
jack outputs) inorder the record what I'm playing.

My problem is this:

When I'm playing the volume level is very well mixed and balanced.  (I
have plenty of volume to hear the music and the DTXpress kit).
However, when I play back the recorded tape, the drum sounds are
almost all I can hear....I can barely hear the aux/in music on the
recorded tape.

Is there a setting somewhere I can change for this or does this call
for a mixer to be attached to better balance the output sound?

(The tape deck is nothing special....just some old Teac analog deck)