This depends on what mode we are talking about here.
Overall volume increase, by +3dB, has gone live for those who have Android 8.0 and up devices, and downloaded the
T+A Solitaire Companion App (Version 1.0.0+66), which featured an OTA firmware update (Version 4.0.5) via the app to connected Solitaire T headphones.
However, though Bluetooth and Bluetooth HQ volumes were on the quieter side, since the update volume is better than adequate loudness wise.
It would be nice to have more, but we shall see.
The real contention is in one of the two wired modes.
Before I get to that, please note that passive analogue single-ended and balanced cables are unaffected by volume issues. This shouldn't need to be said, but I'm erring on the side of caution for readers in general.
Now, the other featured mode of the Solitaire T is USB-C DAC mode. If you took a USB-C cable and connected the Solitaire T to your phone, for example, two things happen. One, all wireless digital circuitry is bypassed. Two, you are using the on-board ESS Saber ES9218 DAC and amplifiers, essentially making the headphones as both a DAC/amp and output simultaneously.
Sounds marvellous, right?
UNFORTUNATELY, it's a mode that many of us have considered to be borderline unusable in its current state as there is an aggressive low volume limit imposed at the firmware level, which is unsatisfactory for listening.
This volume limit is, for example, much, much lower than the two Bluetooth modes, making little sense as to why the non-wireless USB-C DAC mode has such a low volume output.
This is the biggest area of contention for Solitaire T owners.
The other is LDAC codec, but please be patient, as this is in progress between T+A and Sony.
The owners and prospective new buyers are hoping the licencing deal will go ahead and be implemented in due course.
To summarise, the passive analogue and the two Bluetooth wireless modes are working as intended.
Only the USB-C DAC mode has had the biggest, and well grounded, negativity.
It does not, for me, ruin my headphone experience, but is disappointing as this would be a lovely feature to use when I'm in the mood to have a lossless listening session with just my phone.
Hope this clarifies the current overall feedback from us all.
(There are other positive, negative, and in-between comments too, as is with anything, but the above now remains the most outstanding and present issue).