you can't mix them without changing their bpms, what you can do is use the risers as cue points and drop the tune there but a 6bpm gap is very noticeable i think it won't work .

yes u can layer them but it will sound really fucking terrible. and i would not use Reason for audio/wave. Download Reaper but the mp3 in separate channels lower the volume a bit, render and prepare to be really fucking disapoint.