Subpar artificial sounds from the purported JBL premium audio system in the e-Niro 4+ (UK)

[EatSuru]

Greetings,

I just purchased a 21-plate e-Niro 4+ (MY20). The vehicle is excellent, with outstanding efficiency, and I really appreciate it.
Regrettably, I find the integrated audio unimpressive. When playing high-quality FLAC files or connected via Apple CarPlay, vocalists seem thin, and female vocals produce excessive sibilance. The same applies to the DAB radio as well.

I have attempted to alleviate this in three manners:
1 - Reduced treble by -3, increased mid by +1, and similarly elevated bass by +1.
Adjusted the audio two notches rearward to diminish emphasis on the front tweeters.
Folded a black microfiber towel into four sections and positioned it over the dashboard tweeters, leaving the central one uncovered.

None of the aforementioned solutions is optimal or effectively addresses the problem.

Is it possible to resolve this by replacing the speaker drivers, or is the problem with the head unit?
If the issue may be rectified by the replacement of speaker driver units, might someone suggest suitable alternatives and a UK-based business capable of doing this task?

I appreciate your assistance in advance.

[badgx]

CarPlay is unable to play high-resolution music, presuming that is your intention. The Kia infotainment system is likewise unlikely to interpret high-resolution files.

[spiezen]

I have eliminated anything unrelated to this issue.

[MrGreedy]

Test files on a USB drive and play them directly via the Kia system to assess any improvements.

My own use is via radio, and it suffices for a non-technophile such as me.

[Motoman]

Have there been any upgrades to the head unit firmware that impact audio quality? If so, is your Niro 4+ operating on the current software?

[EatSuru]

I have tested high-quality FLAC tracks on USB, nevertheless the harshness remains, although I am on the newest head unit/system firmware from August of this year.
I have an upcoming appointment with a vehicle audio professional and will respond with their diagnosis and proposed remedy. I hope it will just include new drivers and not the head unit.