Muse Hub is a program for downloading Muse Sounds. No other program can download Muse Sounds, so the literal answer is no, you can't replace Muse Hub with anything else.
However, I assume what you really are wondering is if you can use sounds other than Muse Sounds. Certainly - SoundFonts can be used, and also VST3 instruments (WIndows and macOS). So if your favorite Garritan sounds are available in either of those formats, then yes, you can use them.
Comments
Muse Hub is a program for downloading Muse Sounds. No other program can download Muse Sounds, so the literal answer is no, you can't replace Muse Hub with anything else.
However, I assume what you really are wondering is if you can use sounds other than Muse Sounds. Certainly - SoundFonts can be used, and also VST3 instruments (WIndows and macOS). So if your favorite Garritan sounds are available in either of those formats, then yes, you can use them.
With the Aria player you can play all 'old' Garritan libraries.
https://musescore.org/en/node/338162#comment-1156554