First, inserts in every console (mega expensive or cheap) are pre everything except for the gain stage and often times the HPF. Second, inserts are always "pre-send" unless you happen to have one of the few consoles where the direct out level is controlled by an aux knob, which is an excellent feature. In this case as well though, the insert point is still "pre-send". The nature of a "send" is that it routes the signal to a new output in which case would NEVER affect an insert point. Modifying an insert point should not be too difficult from a technical standpoint, but would be a tedious job when dealing with cheaper consoles built on large PCB designs. Typically it just is no cost effective. If you were to modify an insert point to send post Gain, HPF, EQ and/or fader this would be good for recording purposes. If you try to use the console live though it will be much easier to get really bad gain structure happening, and if it were post fader, every fader move would effect the insert. This means that every time you raise a fader on a channel with a comp inserted you would also be sedning the comp more signal which in turn would greatly change how the comp was affecting your signal. If you made an insert post EQ but prefade, then EQ boosts and cuts would also affect the signal that the comp was receiving which in turn would once again change the way your compressor functions and sounds. Basically, an insert is just a pick point for signal. Signal hits the insert and is immediately sent out from the console and then back in and the signal is reinjected back into the channel strips flow to hit aux sends, EQ's etc... In order to modify the insert point, all you need to do is change where it taps the channel at. This can often be done with new traces (usually not a good option due to PCB layout and other logistical reasons) or by adding bus wires to the traces to change the signal origination and return point. On a board that has been assembled the way a Mackie has, none of these points are very readily available to work on without completely unassembling the entire console which may lead to removing (desoldering) many and possibly all of the pots in order to get clean access to the necessary points. On a modular console it is much easier because you can usually just pop out a channel, do the mod, and pop it back in.
