Class D amplifiers are not load invariant. This means that with higher than expected load impedances, they will behave abnormally.
Class D amps use an output filter, and the driver itself forms a part of that filter. If the impedance is different than the intended load, you will have issues.
The Fosi V3 for instance seems to be set up for 4 ish Ohm speakers. And even at 8 Ohm it’s already over-amplifying high frequency content quite a bit, including quite significantly in the 30-50khz region
Here’s a simulation of a class D output filter with various loads. With a 155 Ohm load of tungsten, you could be creating a couple dB boost in the upper treble, with over TWENTY DB increase at 40khz.
L = 11.26uH
Cbtl = 0.703uF
This could mean that at best you’re colouring the sound as content under 20khz is affected, and at worst could potentially cause damage to your headphones or hearing if your amp is pumping high level high frequency content through. And you might not even realise it’s happening, because you can’t hear 40khz, but could still incur hearing damage.
Purifi stuff is apparently load invariant through the use of a different feedback approach, though I don’t know whether the amp will actually be performing as well with a 155 ohm load