Bought a SolP to try it, was very impressed with the sound, but now i'm selling it again because it goes into a too similiar direction of the (more technically capable) Immanis.
My thoughts on its sound:
Two things really impressed me. The bass, both mid and subbass, are fantastic and best in class. It has that super punchy physicality and force that only very few planars can provide, even in the lowest subbass. It also really impressed me with its detail level, i think it surpasses the OG Susvara and the Susvara Unveiled is on par. For its tonality i wish it had a bit more warmth / less analytical sound in the midrange. The darker treble is fine, it's a nice alteration, but i wish it went into a more "old Audeze style" direction with more thickness. But: I achieved said thickness and warmth by just plugging it into my Envy with Western Electric tubes (and also some nice warm drivers). This headphone scales and shifted in tonality, so that i really liked its sound. That being said, its tonality was on the dark, relaxed, and super punchy side, with a huge soundstage. That is more or less also the direction of the Immanis, which is just the superior headphone when it comes to technicalities. The Immanis is faster, more detailed, and in its tonality brighter. I also think vocals are a bit better, but i think that's more subjective and one could even prefer vocals on the SolP compared to a Susvara, especially if you don't like a too aggressive sound. Female vocals were sometimes a bit of a letdown when plugging the SolP into my CFA3, they were sometimes too thinn (but i also have that problem with the Immanis) without any colouration in the chain. I think it really shines on a thicker and warmer sounding amp. On the Envy female vocals were sometimes "only fine", but other times truly awesome, so it also highly depends on the recording.
A weird thing is the treble, it's 90% dark and subdued, which is very fine and a nice alteration, but then there is a peak somewhere in the treble that sometimes makes the SolP sound a bit sibilant, even more compared to the Susvara Unveiled, which is in general a way brighter headphone. Of course this problem comes to the surface way more with not that great recorded music, and i would not describe the SolP as having very sharp and piercing treble in the end.
I also have to say that i don't like the comfort. It's very lightweight, but i get a hotspot from the headband. Maybe i'm an outlyer, could be.
All in all, i really liked the sound of the SolP out of my Envy, it's on another level than the previous TOTL planar which i tested right before, which was the Charybdis, but as i said, the Immanis is set in stone in my collection and the SolP is too similiar in its tonality. I want to mention one more time how impressed i was by its bass, it's probably the second best planar bass right after the 1266TC.
If someone is interested in buying my unit, message me (EU only).