I have (speaker name) and use them to listen to music. They are connected to my Mac min computer. I have herd people say that it is better to turn the volume on the computer all the way up and control the volume using my external speakers (my (speaker name)) for the best sound sound quality. But I have also herd people say it is the opposite. So which way produces the best sound quality?
It can vary case-by-case based on specifics of what hardware are involved. But, to make a generalization, yes it's best to leave the computer's software-controlled volume at max and then control the levels with your speakers / pre-amp / processor or what-have-you.
The reason is that computer operating system drivers are only able to control the volume by decimating the levels with digital signal processing. They aren't actually reducing the power of the signal, but making the content itself quieter. There are varying degrees of quality in how this is done, but they all reduce quality. The result is that the quieter you play out of the software-controlled output, the higher signal-to-noise ratio you will have.
This is also true for an outboard volume control, but hopefully not nearly as much so. That's because most outboard volume controls are either done in the analog domain, so they are actually gaining down an analog signal without altering it's wave, or else at least it's integrated to the preamp processing, which is closer to the final amp gain stage and should still be superior, all things being equal.
It can be a complicated topic and I'm making generalizations and assumptions above that can be picked apart, but I don't want to write an engineering paper.
TL;DR: Control the volume with your speakers or outboard amp, leave computer at max.
PS: This also applies in your car. If you are playing music from your phone, keep it's volume at max and control volume from car stereo.