This compact mixer is perfect for computer recording setups, intimate live sound environments, video editing & production studios, and portable podcasting setups.
You could instead select the other "USB Audio Codec" for Playback Engine, but then you would only get input - no output (fine if you just need to capture something without monitoring then switch back to the other to play back). MultiMix 4 USB FX is a four channel desktop mixer with a USB audio interface that lets you mix live or in the home studio, and record audio directly to a computer. (Still might need to Default your I/O in the Input and Output tabs.)
So try launching Pro Tools with N and select Pro Tools Aggregate I/O for your Playback Engine. Pro Tools Aggregate I/O gets around this limitation by allowing you to combine the Input and Output of your CoreAudio device to treat it as one. 100 28-bit onboard preset effects including reverbs, delays, chorus, flanging and pitch. 8 high-gain mic/line inputs with phantom power, 2 stereo balanced 1/4 line inputs. Compact, affordable 16-channel analog mixer with USB. You can also plug a guitar or bass directly into channel twos switchable high-impedance input. Whether used for mobile or studio recording, the MultiMix 16 USB mixer gets the job done right. You can plug XLR microphones into channels one and two, including condensers thanks to the selectable 48V-phantom power supply. If you are selecting "USB Audio Codec" then that is either just the Input or just Output of your Alesis (sounds like the latter based on your problem). The MultiMix 4 USB FX mixer has four input channels, all of which can accept a 1/4 line input. Pro Tools can only have 1 "device" as its Playback Engine. I have attached another screen shot to show what I see. Can I record each input channel to different tracks in my DAW The Alesis MultiMix 4 USB FX send a stereo signal - a left and right channel signal - via USB to the computer. Channels one and two provide high- and low-shelving EQs, independent gain trims, and have. The Alesis MultiMix 4 USB FX mixer has a USB connection that carries 2 channels of audio from the MAIN output channel of the mixer to your computer. Channels one and two offer switchable high-pass filtering at 75Hz to reduce low-frequency rumble, handling, and wind noise. I do have USB CODEC selected as the Playback engine. The MultiMix 4 USB FX mixer has a two-channel, five-stage, multicolor LED meter for visual monitoring the main output level.
I initially DID have to start with the N key down because I was getting the prompt that the I/O was not recognized (or something like that).