The Mackie 2404 VLZ3 is a 24-channel mixer with twenty mono input channels/faders and two stereo input channels/faders. There are 20 mic preamps.
All aux sends, whether they are pre-fader or post-fader, are post-insert, post-low cut, post EQ, and post-mute. The only difference is whether they are pre- or post-fader. Aux sends 1-2 are pre-fader. Aux sends 3-4 can be set pre-fader or post-fader. Aux sends 5-6 are post-fader (or can be set to send to the internal effects).
"If you insert a TS (mono) 1/4" plug only partially (to the first click) into a Mackie insert jack, the plug will not activate the jack switch and will not open the insert loop in the circuit (thereby allowing the channel signal to continue on its merry way through the mixer). This allows you to tap out the channel signal without interrupting normal operation. If you push the 1/4" TS plug in to the second click, you will open the jack switch and create a direct out, which does interrupt the signal in that channel." See page 30 of the manual for details.
The 4 busses ("groups") have 4 balanced 1/4" TRS line level outputs. Each bus has a post-mix amp, pre-fader, post-compressor TS/RR insert which can be used as a "first-click" direct out.
To get the maximum number of line inputs, use the 20 mono inputs, plus the 2 stereo input channels, plus the 2 stereo returns, plus the tape return (sent to the main mix) for a total of 30 line inputs. But some of these are panned hard left and right. See the following tricks to make some of these mono.
By default, inputs 21-24 will be hard-panned as left and right stereo pairs. Trick to make them mono (panned to the center): Take them out of the l-r mix, assign them to the "group" busses (i.e. channel pair 21-22 to group 1-2, channel pair 23-24 to group 3-4), and assign all the groups to both the left and right main mix. Now these inputs are panned to the center (mono).
The two stereo returns can't be bussed to achieve the same trick (as on inputs 21-24). But, they can be routed to the aux sends. An untested trick: if the aux sends aren't being used, send the stereo returns to an aux send (by means of the "stereo returns" knobs), then patch that aux output to an open input. Pan that input to the center.
Here is the manual.
This mixer weighs 31 lbs (14.1 kg).