Edit: as you cannot reply after your own previous comment on Head-Fi, I'm editing this comment with an update regarding the new firmware and settings. See the end of this comment for that update.
However, please
UPDATE your headphones
ASAP, play a song, then go into the
Sound tab, and select EQ
Custom Settings without adjusting the toggles, as there is a
new bonus feature* I've discovered in testing!
Yep, just noticed the update on the
Google Play Store (v1.4.0+120) but will be playing around with it later today!
So, got the update and installed the firmware.
This is what you see in the app's
Sound Tab and under the
Custom Settings drop-down box. Note: you
MUST have
music playing, otherwise the below new feature cannot be seen/used:

(Note: I have Tidal app temporarily running as a pop-up on my Samsung Galaxy Z Fold5. Phone is in unfolded mode).
Unfortunately, this is not full parametric EQ, with only five pre-determined bands, no Q Factor, and no dB graduation for fine adjustment
*HOWEVER, to everyone using their Solitaire T,
immediately update your headphones and companion app, and set the
Sound EQ to
Custom Settings.
Without any toggle adjustments, you will have a
moderately significant bump (increase) in
overall volume.


This was tested in Bluetooth, ANC, and Bluetooth HQ modes (USB-C mode not tested).
Might as well get your bonus free volume for wireless playback!
This bonus is incredible for dynamics, slam, soundstage, and air (to me!).
This also means I'm lowering my volume listening by a decent factor, but more on that momentarily.
For my initial tests, I used the song
Vermis from the album
Empor by
MEUTE (hyperlinks ought to give you options to stream in your favourite platform). This is an electronic techno marching band who use real instruments live with some synthesised elements for their production albums, though their live performances are extremely powerful exhibitions of live instrument play and lungs.
This track is extremely taxing on audio gear, simply due to the huge dynamic range, expanse of instruments and play, as well as the versatility of the brass and percussion instruments. The bass is very deep (especially mid-bass thump!), whilst the highs, especially on the xylophone, are mellifluous with uncanny decay- again, real instruments.
Back to wireless volume operation, on my Samsung Galaxy Z Fold5 and in the default
Flat EQ mode, I regularly listen between 145 to max 150 (latter usually only in ANC and when I'm doing DIY or lawnmower'ing the garden) in any Bluetooth mode, but predominantly Bluetooth HQ or ANC.
I notice that 149 is where the overall dynamics of the headphones really shine, and replicate much of my balanced passive playback.
With
Custom Settings EQ selected with the additional bonus increase to volume, I can now listen between 140 - 145 and retain the dynamics that previous
Flat EQ @ 149 volume exhibited, in all five steps. This is an entirety new experience, and simply a major bonus feature.
Now, as for testing the
Custom Settings EQ feature further, I wanted to add a bit more warmth to both subbass and bass, leave the midrange as is, and add a small touch to the mid-high frequency, to my overall music playback.
In the new Custom EQ without adjustment and with increase in volume, it's the standard Solitaire T tuning just with more oomph. Nice.
With my settings below, the volume needs to be readjusted lower to avoid clipping or driver instability; at volume 128 - 130 (especially 130), I get the dynamics of
Flat EQ @ 149 volume or
Custom Setting @ 140 - 145 volume.
Unfortunately, 130 is where the drivers start to distort or clip, so
Custom Setting EQ @ 129 volume is my new preference and max. This is brilliant, lower volume and all the dynamics I crave! Well, it's probably not lower volume as the decibels are likely similar to my previous wireless playback, but still, it's nice! I'm sure on quieter recordings that the extra dynamics and headroom (to further adjust volume) is a win for those who were already pushing max volume with the Solitaire T.
In terms of sound quality changes with my new settings, the bass simply hits harder with more textural information whilst simultaneously expanding the width of the soundstage, the midrange continues to be the highlight with exceptional smoothness and body, and my tweaks to the mid-high and high frequency just add a tad more body and sparkle.
This, for me on my initial experimentation, this is closer to my ideal of a sound profile, reminding me much of the
DCA E3 headphones'
frequency response (I still crave for this headphone!).

I'll continue to dabble with the toggles, but even if I set this to no toggle adjustments,
Custom Setting EQ is absolutely
the best way to experience Solitaire T in wireless Bluetooth modes.
It is, to me,
essential.
Or, to be frank, I do not know why the global volume increase is not default, and instead squirreled away under a feature tab
Either way, this has changed my listening experience immediately, and brings the headphones closer to my passive balanced playback setup, something I did not have on my bingo card today!
Enjoy this initial review of the new settings, and hope it gives you good listening too!