You clearly did not understand (and still don't) as evident by your misleading quote here:
Not correct,
lowering the impedance makes them more difficult to drive.
This is a clear cut fact in the case of the GR07, given the impedance curve, which I've linked below.
Again, read my previous post,
voltage drive is no problem for simple sources, it's the current drive that is lacking - and this is what causes lower impedance IEMs to suffer in frequency response.
The visible effect of this problem is that at a few bars of volume, the IEM is already loud enough (with plenty of volume control to spare), however there is appreciable loss of bass depth and control. This is because many portable sources struggle to provide enough
current, not voltage.
Not true, many portable sources will suffer with nominal impedances this low - it is very clear if you perform an FR test with a high current source vs. an average phone or portable.
As I said, the previous-gen GR07C/BE (measured at 43Ω nominal impedance)
were already showing slight bass rolloff issues with a 2.1Ω output impedance source (which is definitely on the lower side for phones, i.e. about as good as it gets on average), so reducing this to 32Ω is in no way a good thing. Yes it's not as bad as some, but also it's definitely a step backwards compared to previous. "Many" IEMs being 16-32Ω does not mean that "many" people's phones are driving them correctly or are sounding as intended.
As a sidenote, the single-driver GR07 exhibits a fairly flat impedance curve (as shown
here, which makes for easier analysis), but on many multi-driver IEMs which claim "nominal 16Ω" at the usual 1kHz frequency, there can be much worse dips elsewhere in the curve causing severe rolloff, usually in bass. So looking at the number alone is not the best idea either, it just happens to work okay in this particular case. I'm intimately aware of this because I own a 2-BA / 1-Dynamic IEM @ "nominal 16Ω" that shows severe bass rolloff issues with average portable sources. It performs great with suitably high-current amplification, but not without. In fact this is why I own the GR07 in the first place, and why many others do too, it plays well with average portable sources.
Read my post again.
I said you can't easily
lower the impedance without changing the driver, it is very easy to
increase the impedance with cables or adaptors.
You are showing a clear lack of understanding on the topic of impedance, which is no issue, but the problem is you are misleading others.