I want to make some basic 'demo' recordings - with 'live' vocals and piano. I have a Mackie DFX-6 - with both Aux Send and Aux Return - would I use one of these and then plug into the line-in of the computer?
Well...it it were me...
Based on looking at the DFX6 outs if you're using the canon (balanced) main outs dedicated to a PA system I'd just use the 1/4 unbalanced outputs to my computer.
But....hopefully you are using an adequate audio interface (preferably with a break out box) with 1/4 or RCA inputs.
If using RCA inputs on your interface you'd just get a stereo 1/4" to RCA line chord.
I'd utilize the Aux Send and Aux Returns for an outboard device if desired or applicable.
I'm sure others will chime in.
That' my brief take on it...good luck.
If it's a "basic Demo" that you're after, you should get acceptable quality by taking a lead from the Tape Out phono sockets to the computer Line In.
You can then monitor what you're recording using either the Main Outs or the Phones Out. The Line In on most modern computers is reasonable quality, unlike the Mic In which is usually poor.
Tape Out will work, but has caveats.
Aux Send would work also, with the AUX1 Send dials having control of volume.
This may give a wider variety of options when recording, say if you want to hear everything from the mixer, but only record the vocals on a given take; you can turn down the AUX dials for all tracks but the vocals. That way only the vocals get sent to the computer.
This would be especially handy if you are using that mixer for computer playback also, since you can isolate what you want sent back to the computer.
Just another option.
Tape Out has all signals going to the Main Mix output in it. So if the computer output is going to the mixer, using Tape Out will send it back in.
Tape Out also has no volume control specifically for it on this particular mixer. The Main Mix sliders do not affect it.
Guess it would depend on the use and workflow here as to which would be used.