Others will I’m sure give you info on the Core and file transfer from Windows, but iTunes is really Windows only now as Apple have made it Music app on Macs for several years.
Highly unlikely you’d be able to transfer from iTunes to Core using iTunes. Someone/3rd party might be able to produce a script of some kind to add new files to the Core but the user base is limited so again unlikely. You should be able to manually access your non-DRM downloads/purchases if needed for backup or transfer to wherever.
Apple really don’t want to integrate with 3rd party audio systems it seems apart from a select few - no reason Apple couldn’t enable iTunes/Apple Music sharing to modern streamers I just don’t think they have the will. Naim have code in place to theoretically allow Airplay of better than CD quality audio to their modern streamers now that Apple Music streaming supports better than 256kbps AAC. Trouble is Apple need to throw the switch but don’t want to it seems.
The iTunes music folder you use (assuming it’s on a Mac) is just a regular folder full of files. You can designate it as a music share and grant access to it for the Core. (At least you can with a Unitiserve and other UPnP servers, so I assume it can be done with the Core too.)
It’s been a while since I tried this, but it certainly used to possible to locate the iTunes music store on a separate drive rather than using the default location on the Mac you use to run iTunes. Assuming this is still possible you could move it to the Core if you prefer.
Alternatively, given that you should have a backup strategy for all your files, having a duplicate of the iTunes store within the Downloads folder on your Core is another option.
I have a MacBook so my experience is not directly relevant. However I am sure others here with Windows have essentially followed the same process as I do with Apple. You need to find the Core as a drive ( in Explorer, I would guess); on the Core, open the Downloads folder and create a new folder for your album that will be transferred from iTunes; (open new Explorer window?) find relevant music files in iTunes; drag and drop the music files to the downloads folder on the Core. To get the album artwork, you need make sure there is a jpg files in the relevant iTunes folder.
I am assuming its like Sierra or earlier. The ‘trouble’ with macs is they are very well made and look modern even ten years later. I moved on a 2016 macbook pro to my niece, it basically looks like a modern M3 macbook, but the hardware will tell you different.
but you have hit the nail on the head, if you are using itunes then your mac by compute standards is geriatric. The biggest issue I have found in this scenario is more and more websites won’t load, believing there is ‘man in the middle’ attacks, when there is not, simply because the OS is just so far out of date.
This all being said, all itunes is doing or Apple music is putting music files into a folder. However downloads form the itune store as far as I am aware will be locked down, happy to be told different, but for rips just drag it over. Contrary to ancient naim lore, don’t rip to WAV, its just a pain in the arse.