“I just want to be able to play my downloaded files as best as is possible.”
If that’s your goal then your Marantz 30n is upto the task. How well your Marantz can curate your library will depend on the size of your library. Go ahead and try it and report back your experience.
For best possible user experience and optimal sound quality of your downloads, consider a streamer like used Aurender N100H and iPad. It’s a modest investment, comes with 2TB of internal storage for your files and you will enjoy the app that’s easy to use.