
Reverb, Delay or Phaser can be dialed up simply by adjusting the pre or post fader knobs located within each channel strip. MultiMix 8 USB FX includes an internal effects processor to quickly and easily add new colors to your mix. A Tape RCA stereo input is also included adding the ability to mix in audio from other sources such as a CD or LP player. New to the MultiMix 8 USB FX is a high-impedance input on channel two, which allows direct connection of a guitar or bass this is a great convenience for singer/songwriters looking to get a clean, "hot" signal. TRS Line inputs are also available on all eight channels of MultiMix 8 USB FX. These XLR inputs also have a switchable phantom power option to accommodate both dynamic and condenser microphones. MultiMix 8 USB FX features four XLR inputs with independent gain pots on channels one through four. Offering microphone inputs with phantom power, guitar-direct inputs, and line-level inputs for connecting everything else, plus a wide range of effects, the MultiMix 8 USB FX delivers clean audio to your PA or recording system plus hassle-free computer connection. Whether you are mixing a band or sub-mixing a group of inputs, such as a drumset, the MultiMix 8 USB FX is easy to use, rugged, and packed with features. This compact mixer with built-in effects doubles as a computer recording interface so you can mix, record, or do both at the same time.

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).Record, mix and add effects all in one place. (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. 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). Pro Tools can only have 1 "device" as its Playback Engine. I have attached another screen shot to show what I see.

I do have USB CODEC selected as the Playback engine. 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).
