we hear everything in stereo.
however,
most (
acoustic and electronic) sound sources have a
single point of origin. We place it in the stereo field based on where we are positioned (and therefore our ears are positioned) in relation to the object. It is the time difference between our ears that tells us the location of the sound source (the nearer ear hears the sound first, the delay or inter-ear delay between the near ear and far ear will be variable within the context of distance, but a fixed value based on wavelength and the actual speed of sound for the current medium).
when we come to do this electronically, we use a panning pot to change the perceived intensity of the sound as it sent to each side of the stereo spectrum i.e. we increase the intensity on the left side and lower it on the right side when we pan a sound to the left and
vice versa rather than use delays to create the same outcome as our ears experience naturally - in the past this has been because it was difficult to create an easily adjustable finite delay on the order of 6 microseconds to 6 milliseconds, as well as the difficulty of creating it as a (finite) multi-band ,multi-delay
system; today it is because it would require a complete change to the way we create the illusion of space and distance.
the Haas-Effect can be used to a small extent in creating a faux stereo separation on some sound sources. However, the true nature of Haas's observations was that people would introduce a 10db increase in intensity on the side that seemed to be further away (delayed) so as to make it seem that the left and right ears were hearing the same sound as a mono sound source - i.e. Haas's studies were designed to identify and account for intensity adjustments required to convert a stereo signal to mono. The inter-ear onset times that Haas used were in the order of 2ms-50ms
to your redrum issue
the line mixer serves no useful purpose that I can understand in the scenario you describe, that 14;2 mixer could not do better. Do you have a link for the video?
I would be inclined to use the fx as inserts between the output of the individual redrum instruments and the mixer. Alternatively you can use a single 14:2 mixer for each instrument and fx returns after splitting the signal to each fx unit if necessary, then hook each of the individual 14:2 mixers to final master 14:2 mixer
create your stereo image using the individual 14:2 mixers and leave the eq on the master mixer off and the panpot for each channel in the center position