There’s a lot of info on the Stellar P3 in this discussion:
Stellar Range Power Regenerator
I asked about the differences between the new Stellar P3 and my old P3. The reply excerpt below pointed out the technology improvements and sound improvements of the Stellar P3 compared to the older P3. The same logic might apply to the Stellar P3 v. the older P5. Hope this helps.
"On the other hand, The P12 and P15 sound better than the P5 and P10 and not by a small margin. What we learned from making the P12 and P15 carried over to the new P3. Things like an improved output stage that offers exceptionally low output impedance and a world class sine wave generator.
Plus we managed to make it fanless.
All things considered, the new P3 is an improvement over the old."