As @
Monotremata
mentioned, your MOTU interface has also own low-latency mixer.
That's the way to monitor inputs without DAW involved. You need to go to AVB mixer, enable particular inputs at left side of UI, which will create new corresponding faders in the mixer and route input audio there. Faders can be left in unity gain or you can adjust balance according to your taste. Be sure to add also channel for DAW playback (eg. from computer 1-2) to the mixer.
Then you need also to route mixer main output to two analog output channels, where you have your monitors connected. You can do that in routing pane at cross point matrix. Stereo signal coming from mixer will replace your previous direct routes from DAW, hence you need to add this input from DAW to mixer to hear it.
That should be enough to monitor inputs without a DAW.
Finally keep in mind, that you can't use both software and hardware monitoring together, otherwise you'd hear sounds twice (once before audio reach the computer, the second time as it pass through DAW). DAW monitoring is definitely necessary, when you record some amp sims or generally using monitor through native plugins. OTOH hardware (direct) monitoring has also own advantages, because it has lower latency (doesn't depend on working buffer size), so if you don't mind to hear inputs without native effects (you can still use ones in MOTU mixer.. EQs, comps, verb etc.) for recording, that could be preferred.
So if you will be monitoring through DAW, then simply mute respective channels in AVB mixer.. or you can solo just stereo input from DAW, which effectively mutes everything else there.
Michal