For "simple" applications where the requirement is to add a live mic to the output produced by PlayIt Live there are relatively few products on the market which are well suited to the task.
Yamaha produced the AG-03 and AG-06 with the "Podcast", "YouTube" and "Live Streaming Gamer" market in mind.
Compared with larger music or radio mixers and audio interfaces it has a few unusual features. Sound On Sound did a good overview review when the products were launched:
Using the Yamaha AG-03 and PlayIt LIve it is possible to make a simple radio setup which works well.
The minimum system would be a microphone, laptop, headphones and the Yamaha AG-03.
Install the Yamaha drivers and separate "configuration" software for the AG-03 before doing anything else.
The Yamaha AG-03 has a USB sound card, and I've set the "TO PC" sound to "loopback" which means that the sound from the PC (PlayIt Live) is returned to the PC mixed in with the microphone.
Other applications would require different settings on the "TO PC" switch but this is the seeing for this application.
The other key setting is to have "MONITOR MUTE" off (or you won't hear the microphone in the headphones when you speak).
Then set PlayIt Live to send the audio from the players to the AG03 (I wasn't using the ASIO driver but that would probably be first choice)
Then set the QuickCarts to the same output.
Finally, set the track audio editor to something else (so it won't come out on the "live" audio)
At this point you have a setup which will play the audio from PlayIt Live to the mixer, the level of the PC audio is controlled on the control with a picture of a PC and it is possible to mix in the microphone on the linear fader.
Personally I quite like the default microphone compression and EQ (bass roll off and some limiting) and I found that even with a phantom powered mic I needed the gain quite high.
"Line up" (such as it is for something without meters !) seems to be where the bolder lines are on both the mic and PC faders, leaving a bit in hand.
You could record the output of the mixer into Audacity (or similar) or use streaming software (either the plugin for PlayIt Live or different software) to take the mixer output.
The "metering" is two lights. The green LED lights when there is any significant audio (assuming the PC fader is at "line up", the red light will very occasionally come on with music or mic peaks (once again with the mic set to line up and peaking to what seems a reasonably sensible mix against the music level).
All in all, this is a simple and capable mixer for one presenter and PlayIt Live.
The Yamaha AG-03 will power from the PC (don't use a hub) and works well.
I don't recommend my HP Mini for PlayIt Live. It's very under powered and will glitch if Windows gets distracted but it's what I have to hand !