If you want to playback more than 8 recorded audio tracks, export your audio tracks as .wav files, then re-import them as "samples".
1. Go to Browse and tap the Places tab.
2. Select the drive where you exported the audio track.
3. Select your exported track and tap Load.
4. Tap the Sample Assign tab and assign the sample to a pad.
5. Go to the Main screen.
6. Press the Record and Play buttons to start recording.
7. Hit the assigned pad on beat one to trigger playback of your exported audio track from the beginning of the song.
Note: If the sample/track does not play back in full due to the size of your sequence, press the Main button and change the number under the Bars field to a greater number.
8. Once your pad hit has been recorded as MIDI data, your track/sample will be played back each time you start the sequence.
Once the track is assigned as a sample in your project, you can delete the old recorded audio track to make space for a new one. MPC standalone has a 128 track limit for MIDI, so you will have plenty of space.