playing over a recording

Can anybody help? I am using audacity to record Guitar and I have just imported some backing tracks into audacity. I want to play these tracks and record my Guitar over them. I want to hear my guitar playing and the backing track at the same time? It only seems to let me do one or the other??

“Edit > Preferences > Audio I/O”
Select “play other tracks while recording new one”
Do not select “software playthrough”

External sound cards do not always support this option.