Re: record existing audio tracks into a new audio trac...
The easiest way to render multiple tracks to a single audio file is to use Logic's Bounce feature:
1. Solo the tracks you wish to "bounce" into a single audio file.
2. Choose File > Bounce...
Make sure to bounce to aiff or wave and if the original recordings are 24 bit, then choose 24 bit and keep the project's sample rate. Set the start and end point you wish to capture to an audio file.
3. Also, tick the "Add audio file to project/Bin" so you can easily locate the new audio file - and decide whether you wish to use real-time (slower) or offline (quicker).
4. Hit "Bounce"