There seems to be a lot of misunderstanding, so lets break it down:
The (2) is, again, non logical - as I have spent some effort on my previous reply to explain to you, such a thing doesn't exist. You CAN NOT connect a BT IEM (any BT headphone) to a DAC/AMP via BT. No chip maker even developed a BT chip that can allow for such function nor does any DC/AMP maker ever attempted to ever design such a thing. What you are asking on (2) is a fantasy setup that never exist before, nor even likely will.
The output of any DAC/AMP is almost always analog signal (*there are exception with some also outputs SPDIF or Toslink, but NEVER BT). Your assumption is fundamentally based on an erroneous idea that never really exists in the real world.
Again, No such a thing as a "DAC/AMP to can connect to IEM via BT". You are asking people to suggest to you a thing that doesn't exist.
By 'DAC/AMP', we are referring to a headphone amp that also comes with a DAC - which is short for Digital-to-Analog Converter. As the full name suggested, it only does one thing: converting digital signal to analog, not the other way around. A DAC/AMP with BT function has one extra set of BT chip, which takes the BT signal (* = digital) from a smartphone or any BT source, and feed it into the DAC in order to convert it to analog signal, then the amp section amplifies the signal to feed it into the headphone - in NO way you can somehow magically turn any path of the process back into a BT signal unless you use an ADC (*analog-to-digital) circuit - but that will be extremely stupid. The reason is, as I have explained on my previous reply, doing so only cause degradation of signal due to multiple decode/re-encode. There is no benefit to make a device that purposefully decrease SQ when you can just send the BT signal from smartphone to the BT headphone directly.
A DAC only takes digital and convert it to analog. An amp only take analog signal and amplifies it. You COMPLETELY misunderstand how a DAC/AMP works and just assume it will somehow magically convert whatever you want to any other signal you want - well, it doesn't work that way.
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In any setup, there will always be a bottleneck - for example, if you smartphone only output poor quality SBC codec over BT, somehow you use an BT enable DAC/AMP to convert it to analog signal, then you feed that analog signal into an ADC and resending it over BT (*such a device will be called a BT transmitter), perhaps even using LDAC, then your BT IEM received the LDAC signal and covert it back to analog and feed it to the transducer.
Now the reality is your original music already suffer a lost of quality when it was first send over SBC, then it suffered a 2nd lost of quality when you using an ADC to convert the analog signal to back to digital, then another (minor) lost of quality by sending it over LDAC (note: even LDAC is not a completely lossless codec). Lastly, the DAC inside your BT IEM need to convert the LDAC back to analog and likely it is not going to be a very good DAC due to the size restriction of the circuit inside the IEM, so another minor lost of quality there. In the end, what you really are getting is a process that results in the accumulation of four lost of quality. In comparison, you need suffer 2 lost of quality if you just connect your smartphone to your BT IEM directly.
The takeaway point is, you should stop trying to complicate your BT setup with non-existing dream-up device. The best way of is to get a LDAC enable smartphone and a LDAC enable IEM, then connect them directly. END OF STORY.
