To your numbered questions…….
Definitely not the 1.
I’d – in that case – probably go for 2………although I am not so sure that it always will be significantly better.
As for controlling the volume via the Core – yes, you can do that – there is a setting just for that.
3. would be an extra not necessary step…..unless you’d like to run the BL18 wireless.
When you used your Mac/Music, your source material probably was regular 44.1/16, that then was upsampled to 48/24 in the settings there, right?
When you compare stuff from two different music services, you can not be sure that the mastering is identical (Apple has their own rules there).
This means that – if you want to do a comparison between an analog connection and a digital – there are many variables. First of all the source material has to be exact the same and also the SPL (the volume you listen at) must be identical. In real life this can be very complicated and can easily lead to ‘quick conclusions’.
The ‘DAC’ in the BL18 is not just a regular DAC like you often see as a device in setups with a digital source and an analog input. It is much more an integrated part of the sound processing in the speaker….I am sure ‘someone else’ can explain this better.
All processing there is based on a conversion to 24/48 in order to keep the sound consistent with all inputs.
IMHO you should not worry that much about sample rates and bitdepth. Even source material in 44.1/16 can sound excellent depending on the actual recording, the mixing and the mastering – a higher bitrate/bitdepth is by no means a guaranty for ‘better sound’.
I recomment that you try listening to what you normally listen to with an analog connection (PL/good shielded PL cables) and with an optical connection from the BS Core for a while……in order to see what suits you best.
Remember that…..when it comes to audio gear, cables, sample/bit rates etc – it is not about ‘good or bad’, it is much more about ‘different’……..unless you – of course – have really bad stuff.
After all it is about you liking what you hear and not about which sample rates/bitdepths and cables you use.