I'm sorry, I can't give a quantitative comparison. I do have a 3P with premium interior.
In the X I asked for a song using voice control, and it came on, and I thought "wow, this sounds WAY better than the 3!" It definitely has more bass -- I'm considering turning the bass down in the X whereas I would have asked for more of it in the 3. It seems to have more overall power -- more sound from a lower volume setting -- though the quieter cabin may be contributing as well. But those are like two random factors I happen to be able to put my finger on that don't really represent the "wow this sounds WAY better" factor.
I normally listen to Apple Music files copied onto a USB drive. I'm stuck right now because I went to load up a drive for the X and discovered I've added over 100 songs to my main playlist, but I'd have to buy them one by one on my phone to get non-DRM versions for the thumb drive. What a pain (and unnecessary expense)! It seems dumb to complain about adding $150 of music to a six-figure car, but nevertheless I wish Tesla would natively support Apple Music... or start the App Store so one of us could do it ourselves.