Recording onto different tracks in Audacity

[linux_matt]

I use Audacity to record live piano together with a backing track. The digital piano sound goes into the "line in" of a Soundblaster card and the backing track is either played via mplayer or else it is already present in Audacity. The Recording device in Audacity is set to "Sysdefault line". When I start recording in Audacity the backing track and the live piano are recorded onto a single track. However, I would like the backing track and the live piano to be recorded onto separate tracks so I can adjust the volume of them separately. Is this possible using the setup I have described? Thanks