Hi - if you're having trouble, please ask your question. I don't completely understand what you are asking.

If you are download and installing a full UltraPAK - absolutely that is a huge install. You can install that either on an internal drive or external drive - either way will work. If you are using the Install Manager, you can choose your install location under the "Select Destination" drop-down menu. You also need to pay attention to where the installer packages are downloaded to, which is on the left side (Download folder). That can be an internal or external location as well. There is a tutorial and FAQ section here:
https://www.pgmusic.com/download-manager-mac-help.htm

If you are installing an individual package and it says you need to install it on the macOS system, that is an Apple installer.app issue, and it should be resolved by simply running the package again, only running one installer package at a time,or if that doesn't fix it you might need to reboot. You should be able to select any volume.


Andrew
PG Music Inc.