Repeat the first tutorial but do not stop recording BBC Radio 1.

In the File menu, select New iRecordMusic. Alternatively, press Option-Apple-N. This will launch another copy of iRecordMusic which will act independently of the first.

In the new copy of iRecordMusic, repeat the first tutorial but select a different radio station, such as BBC Radio 2, and start recording.

You will notice that you are hearing both streams at the same time on your Mac. In one of the copies of iRecordMusic, select the menu option 'Mute' to silence the application. This has no effect on the actual recording. You could mute both copies and listen to something in iTunes instead, if you wanted to.

Congratulations! You have just recorded multiple streams at the same time - 1,2,3,4 or more streams, it's up to you!