Hello fibonacci11618,
The PS will develop its soundstage different then your Sigma OB. With the PS you will get a deep depth of the stage, like your Sigma OB's, behind the speaker and a certain percentage will also project in front of the speaker more then the Sigma OB. You will experience this at sitting a few rows closer to the stage of the instruments. I believe the PS will be a much more dynamic sounding speaker (faster/harder hitting) with more clarity/micro-dynamics without becoming less musical. The PS does not sound "boxy" at all, so I don't think you would feel you went back to the "box enclosure sound" at all with gaining what I mentioned above.
The PS will develop its soundstage different then your Sigma OB. With the PS you will get a deep depth of the stage, like your Sigma OB's, behind the speaker and a certain percentage will also project in front of the speaker more then the Sigma OB. You will experience this at sitting a few rows closer to the stage of the instruments. I believe the PS will be a much more dynamic sounding speaker (faster/harder hitting) with more clarity/micro-dynamics without becoming less musical. The PS does not sound "boxy" at all, so I don't think you would feel you went back to the "box enclosure sound" at all with gaining what I mentioned above.