Help! New to RPi streaming and in over my head

It sounds as if you are attempting something that just can't be done. Autoscanning for your iTunes music will not succeed. Neither Moode nor Volumio will enable you to play files stored on your IMac unless you send them over Airplay or UPnP. Your music needs to accessible via NAS or be stored in a USB drive attached to the Pi.
I think you could do what you want if you install a server on your Mac such as LMS, but I have no experience with that. Perhaps others could advise.
 
I want to use my Itunes music
...
I know the Imac ip address, and I have the path name to my music folder
iTunes and Apple Music use a quite conventional folder structure, so it should be perfectly plausible to share the iTunes folder as an SMB/CIFS network share ...
unless Apple has deliberately put some roadblocks in place due to music copyright issues (?).
I think a better place to ask your question would be the Volumio forum, but I can offer this: you should pay some attention to the network share device's configuration, before moving on to Volumio setup. This means setting up your Mac to correctly share the iTunes folder. See here -
Share Mac files with Windows users - Apple Support
In particular, consider setting up a user account on your iMac specifically as a network share account.
 
Hi linuxfan: Thanks for your follow up.
No I'm not. Loaded music onto a thumb drive to plug directly into rPi and have been playing this way, but way more cumbersome.
Audirvana works fine, and I was attempting to compare Audirvana to Volumio/MoOde/etc, but cannot get them to play nice w/Mac. Only limited Google leads to track down this problem, but i am not alone with issues with Big Sur.
 
I don't own Macs but if a Mac can share files with Windows, I suppose it should be able to do it also with Linux. Wait... my QNAP NAS uses Linux and allows Macs to connect.

I had problems first creating a Samba share on my Picoreplayer RPI. It would nor accept my credentials. Had something to do with the LSA version on the windows side.
Another thing is.. every time You try different settings, reboot the RPI in order to validate the new configuration.

Try a Linux networking forum for help.