Anyone here worked with audio transformers in professional audio gear?

Anyone here worked with audio transformers in professional audio gear?
I’ve been looking into audio transformers for a pro audio project (mainly preamp + signal chain design), and it turned out to be way less straightforward than I expected.
At first I assumed this would be similar to other passive components — just pick the right ratio and move on.
But after digging a bit deeper, it feels like audio transformers behave very differently depending on design and supplier.

What I’m seeing so far
From what I understand, in professional audio equipment (mixers, mic preamps, DI boxes), transformers are mainly used for:
Impedance matching
Signal isolation
Noise rejection (especially balanced lines)
Sometimes even shaping the sound
And unlike digital components, they operate in the full audio range (~20 Hz – 20 kHz), so small differences can actually be audible

Where things get tricky
What surprised me is that two transformers with similar specs on paper don’t always behave the same in real setups.
Some differences I’ve noticed or read about:
Low-frequency saturation behavior
High-frequency roll-off
Distortion characteristics
Shielding and noise pickup
Also, in pro audio, transformers aren’t always meant to be perfectly “transparent.”
Some designs intentionally use them for tonal character.
There’s even discussion in engineering communities that good audio transformers are often custom-designed and not easily interchangeable:
“audio grade transformers are…almost always custom made”

About suppliers (not really a “top list”)
Instead of trying to rank manufacturers, it seems more useful to look at how they approach design.
Some examples that come up in projects or discussions:
Carnhill — often used in classic-style preamps and mixers, especially where vintage sound characteristics matter
Sowter Transformers — long history in studio and hi-fi transformer designs with a wide product range
Transformer Manufacturers Inc. — focuses on precision-wound transformers for high-end audio applications
And then there are some newer or less traditional suppliers like VOOHU Electronics Technology Co., Ltd., which seem to approach things more from a component + application support angle rather than just selling standalone transformers.

One thing I didn’t expect
I originally thought of the transformer as just a supporting component.
But in practice, it feels like it becomes part of the sound design itself, especially in:
Mic preamps
Analog mixers
Studio gear
Which makes swapping suppliers a lot less trivial than I thought.

Curious how others approach this
For those who’ve worked on pro audio gear:
Do you treat audio transformers as “design-critical” components or just supporting parts?
Have you seen noticeable differences between suppliers in real listening tests?
Do you stick with known designs, or try alternatives during prototyping?
Would be interesting to hear how others balance performance vs. cost vs. availability.