Thanks for sharing. I’m not too sure on the technicalities but my ears suggest this could be right, there is just no difference whatsoever.I can totally understand that. I had the same issue with the Moondrop S8 and if you compare the graphs
The Monarch Mk2 and the Moondrop S8 are both All-BA (EDIT: the Monarch is not an All-BA Set, don't know why i wrote that, forget that it has no relevance anyway) sets with recessed lower mids and pushed upper mids/lower treble. That is meant to create an pleasing and fun sound and also sound kinda neutral/flat at the same time and reveal a lot of details. So it tries to be an best of all worlds but this does have negative side effects.
The biggest difference between the Waklman and for example the BTR7 (or M11 Plus ESS which sounds almost the same) is the realism of for example percussion instruments or the high speed.
But with recessed lower mids and pushed upper mids/lower treble, you pretty much kill that advantage.
With the IER-M9 for example, there is an pretty big difference between the Walkman and the BTR7, especially with acoustic instruments, and if you compare the graphs, you can see why
But most Audiophiles love recessed lower mids and pushed upper mids/lower treble as it makes everything sound extremely clear and detailed. Its the same with modern TVs that all have an blue tint because an natural/real white (which is just normal, perfect white) is percieved as "warm" which makes colors less pop and gives an kinda oldish look.
And its the same with Earphones and Headphones. This "colder" more detailed sound feels more modern to a lot of peopls, but at the same time, you loose a lot of informations that are essential to notice the difference between such two DAPs.
Or to use a different meatpher: If you put enough ketchup and mustard on a sausage, you no longer notice how good the meat quality is.
I will do some A/B testing (WM1AM2 vs BTR7) with my IER-Z1Rs now.