Time/Audio Track Stretching

Select all audio tracks and Ctrl-select Transients in the Edit Filter of one track to enable Audiosnap on all of them. Set the Clip Follows Project mode to Autostretch in the dropdown to the right of the button in the AS palette, and then click the button. All clips will get a red double-ended arrow on them, indicating autostretch is enabled.

Now you can add a tempo change at the beginning of any section you want to slow down, and a change at the end to return to the original tempo. The audio will retain its relationship to the timeline. The Now time will just travel faster or slower according to the tempo setting. Because MBT time is the fixed visual reference in SONAR, you won't actually see any change in the audio as it "stretches", except for a slight redrawing of waveforms in some cases.

Quality is in the ear of the beholder. Initially, you'll be hearing the Groove Clip or Percussion algorithms that are used for real-time non-destructive stretching. Once you ge the tempos adjusted, you'll want to bounce each clip down to render the stretching permanent with one of the so-called "offline" stretching algorithms to hear the final result. You can set a different algorithm for each track appropriate to its content.