Pure Direct, Direct and Straight means the AVR bypasses the Tone Controls, EQ, DSP.
You can still bypass the Tone Controls, EQ and DSP in Stereo Mode.
When you bypass the Tone Controls, EQ and DSP in Stereo Mode or usePure Direct, Direct or Straight mode, the sound may seem identical to you when you are just listening to music or watch videos.
I can tell you that when I do karaoke, Pure Direct and Direct have no delay in sound, but Stereo Mode has a few seconds delay in sound. This tells me that Stereo mode has some kind of additional processing, which causes the delay in sound. But Pure Direct and Direct do not have additional processing and hence no delay in sound (
even when I do Pure Direct + LFE + Main which sends bass to the subwoofers) with karaoke.