Can’t see this mentioned yet. It would be great to be able to select ‘internal playback’ as the sampling input. It’s a great way to mix and match tracks and them bounce them into a single sound or loop.
The Pioneer SP16 actually implements this very well - you can for example select a 1bar duration (options are 1/4 1/2 1 2 etc), and ‘play’ as the trigger to sample, meaning that the start of the recorded sample is spot on. By muting and soloing tracks it is easy to build new sounds by messing with other tracks.