I am currently running Mopidy w/Moped on a Raspberry Pi 2B. I’m not running it as a service. I don’t have a DAC or AMP hat but will be adding those down the line once I’ve verified I can play back audio as I would like to.
I would like to have the pi run headlessly but be able to control playback on the pi with a tablet or a phone on the same (wifi) network.
I see on Mopidy’s site the option to run Mopidy “as a service” but I am unclear whether this means that I would control Mopidy remotely as I wish or whether I would playback music on connected devices by connecting to Mopidy as a server. Or something else 
Lastly, and I realize that this isn’t covered by the title of my post can someone simply confirm for me that I would be able to expect higher quality audio if streamed from a DAC card like those made by HiFiBerry. Again, I just want to confirm that if audio is going out via the card rather than the headphone jack the signal wouldn’t contain so much noise.
Any help is always appreciated. Thanks!
David
Running as a service means it will run in the background and start up on boot. If running as user you need to start it by using mopidy in a terminal window, once the terminal window is closed mopidy also stops, therefore to run completely headlessly it needs to be run as a service. As far as I can tell, mopidy operates the same way, but the config file is in a different location.
You can control remotely and playback through the pi mopidy is on, alternatives like snapcast, to fill the home with sound, are also available.
I use a couple of phatdac on Pi0 but my ears are not so good so can’t confirm sound quality - it saves having usb connections into Pi0 and keeps a smaller package.
So just adding to what @Steve_Lambert has already said: out of the box, Mopidy’s audio will be played on the same machine the server is running on. If you want to send the audio over your network to other machines then you can see the icecast setup at https://docs.mopidy.com/en/latest/audio. Or, install and configure snapcast as Steve says.
As to audio quality, the latest raspi-config should include an option to use the new and greatly improved onboard audio driver. Make sure you test that out before spending money on DACs.