Monitoring previous tracks in headphones

[len22]

I am having a problem hearing the previous tracks laid down in my headphones while I am recording a new track.
Yes, I've checked Monitor line input.
My setup is this....
Behringer X18 digital mixer into the PC and using waveform free.
Ive tried plugging my headphones into the headphones of the mixer...no go.
I've also plugged the headset into the input jack of the wireless monitor. (which is connected to the x18 aux 1)... Doing this I can hear myself as I record a track but not the previously recorded tracks.
thanks

Win 10
PC with Behringer X18 acting as the Audio interface. Hooked up Via USB