What is the best place to archive my digital music files?

For best sound quality no need to incorporate anything from Apple. Use Qobuz with a dedicated streamer. You can start cheap with a WIIM minihttps://www.wiimhome.com/wiimmini/overview

from there, the world is your oyster when it comes to network streamers. I am a particular fanboy of INNUOS and their pulse series of music players

just a sidenote You can use your Apple phone as the remote for streaming, I was referring to anything that uses AirPlay derogates sound quality. 

Why do I need a Network Streamer when I can stream from Qobuz directly from the Marantz?

Not sure how the Wiim device would add to my system.  Thanks. 

Last time I used HEOS app you couldn’t get Qobuz. So with that said, you would not have a need for the WIIM device. Now with that being said, if you’re after better sound quality in your streaming a separate streaming device such as a INNUOS pulse mini https://innuos.com/pulse-series/

OP

your original post is to short on information.  What is your current source for your digital files?  Does your Marantz amp come with a streaming module?  Does it have an included DAC?

  If the answers to the two questions above are yes, then does the streamer-DAC accept Qobuz directly?  Or are you using a PC that is attached to the DAC by USB?  Or sending Qobuz from a portable device to the amp by Bluetooth or AirPlay?

  Regarding your iTunes files, presumably everything in there is available in Qobuz.

If you ripped CDs or saved downloads into iTunes, and you want to keep a physical copy , just keep whatever device you are currently storing them in , and make sure that you have a backup.  If you were to add Apple Music, then all your files will appear there.