Magico S5 Speaker - SET UP ADVICE PLEASE - Tow-In - Etc.

I would think that this combination of gear, DAC/Amp/Speaker would have a very strong, detailed, but potentially bright sound. I'm not surprised that you are getting that result. I  have no issue with Pass Labs; I have reviewed them and used them extensively, but I would think a Pass/Magico combo would be tough to work with.

A friend of mine who had trouble with too much stridency and upper end energy with a Pass/Thiel combo put in a CJ (Conrad Johnson) tubed preamp and that has been a lovely combo. So, perhaps a warmer sounding preamp in the chain could help. I know from experience that often when going direct from DAC to amp it can be very tricky to get the tonal balance correct. In fact, most DAC to amp pairings require a fair bit of adjustment. So, no need to despair; it's really fairly common.

When you have that much of an issue often one has to change components, not just cables.

One thing you can try; you already have the subs. With many systems adding subwoofers can ameliorate a perceived overemphasis on the high end. It balances out the spectrum and it is amazing how the addition of deep LF makes extension on the top not as glaring. So, I would try the subs with the speakers as a first step.

If you have some additional interconnects, try whatever ICs you have on hand. Often a very good combination can be found where the IC - as an easy change - can address some high level stridency.

Also, if you have different brands of power cords, rotate them between gear. The results can be helpful.

These are among the simplest and easiest changes. If doing all this does not seem to improve the situation enough for your taste, then you are looking at either a speaker or component change. Or, you can swap out entire looms of cables to find some that mesh better with the system.

Regarding positioning, toeing in the speakers or not is entirely your option. I would not simply place them parallel, but would experiment with some toe in, because it influences the center image and that image in relation to the soundstage. Even if the manufacturer says no toe in is necessary, still try it, as you may prefer it.