Is a preamp necessary for performing live?

There are already very nice preamps in your Duet. If you are happy with your recorded sounds for vocal and guitar/bass, you are great for live. Some guitars and bass do benefit from a preamp (a tube preamp is nice for adding some warmth, for example), but this is not "must". If you have a weak signal from an instrument, a preamp will help boost that before going to your interface.

The main limitation of the Duet will be the number of inputs (just a mic and a guitar, for example, unless you use a premixers before an input(s)), and the number of outputs. To move beyond that and get more flexibility, I suggest a MOTU Ultralite (many inputs and outputs, plus built in hardware reverb, compression, and eq).

The amp sims in MainStage/Logic sound great for live performance, although they do eat up some CPU and memory. Play around with using Pedalboard followed by Amp Designer in your guitar and/or bass channel strip. Experiment with the settings (start with presets and tweak). Again, trust your ears! Keep working on your sound until you get it where you really like it ..... then your audience will love it.

Thanks for your kind comments, and glad to help. Yes, the Ultralite would replace your Duet for live use. I keep mine in a small "road case" that is prewired with all my input and output cables; my Duet stays safe and happy in the studio.

To do a separate mix for your monitor(s), you could 1) create a bus channel/aux channel strip for your monitor send/output, 2) your cabling goes from that specified output channel to your monitor(s), 3) in each instrument channel strip (including your metronome), select a send to the monitor bus, and use the send setting as your "mix" level, 4) use the bus level as your overall monitor volume. Read your Logic/Mainstage manual for more info on using aux channels and busses ..... they are VERY flexible and useful.

{quote:title=dingdangdawg wrote:}The amp sims in MainStage/Logic sound great for live performance, although they do eat up some CPU and memory. {quote}

I find that I can get a very good tube like sound without using the amp sims; just experiment with the Channel EQ settings then add a small amount of Stereo Delay (the preset 'Vocal Enhance' at about 25% is good) plus a judicious amount of Space Designer. For guitar, I find the preset '1.4" Percussion' is usually a good starting point. Put both of these in a bus, Delay first, & set the guitar send to somewhere between -6dB & -3.5dB. If your EQ is set correctly, this will give a beautiful clean, warm sound to start building on. Any of the PedalBoard overdrives will give you good results on this.

One small addition to dawg's excellent summary - set the send to 'pre-fade'. That way, changes to your front-of-house mix levels don't affect your monitor mix.

Excellent addition, littledeen, I forgot to mention that essential point.