Update
Placing the ls50s upon Isoacoustics stands did make a difference, mostly in a more open soundstage and tightening the bass a bit. So I’m glad for that!
I do have a no ice question though. Can someone please explain why changing out the Dac in the system won’t have an audible difference? I’ll describe the system a little better.
I use AirPlay to send Prime (HD) music to Moode on the Allo Digione Signature, the output is through coax cable to the Schiit Modi DAC. Then it goes to a Schiit SYS preamp, then to the Red dragon power amp, and finally to the passive ls50
The DAC doesn't affect the sound signature, because it's supposed to simply convert the digital signal into an analog one. Any $2 DAC chip these days should be able to do that with transparency and near-perfect linearity. (and even 0.5 dB variance would be really nothing compared to what you get by simply moving your head a couple inches to one side or another!)
A usable DAC will have beyond 100dB SINAD, whereas speakers and amplifiers are nowhere NEAR that level... the DAC simply doesn't affect the output in any audible way.
Over the past 10-15 years, we haven't really seen any worthwhile upgrades in DACs that would warrant a Eureka moment.. they were transparent back then, and they still are.
Of course, if the DAC has DSP built-in, like differenf filters, EQ settings, etc. then it's not just a DAC anymore.
Your issue with the speakers being too strong in the highs can easily be resolved: just reduce the toe-in slightly. (instead of pointing them straight at your ears, have them point slightly more outwards, if not straight away from the wall. (this article explains it nicely:
https://www.stereonet.com/au/features/speaker-toe-whats-it-all-about )
That the isoacoustic stands helped with bass is weird.. they are supposed to isolate the speakers. Unless the surface they are on strongly vibrates along, isolating the speakers shouldn't "tighten" the bass, because the speakers can resonate more after being isolated. If you want more precise bass, you ideally want to COUPLE the speakers to a very heavy base.
E.g. use metal spikes and place the speakers on heavy stone plates (like granite or marble, etc.) then put those stone plates on foam pads to decouple/isolate them from the desk.
That way, the speaker will transfer all the vibrations from the enclosure into the stone and the stone, being a very heavy mass/high density, will simply absorb it, because it doesn't start to resonate at these low levels.
But if it sounds better, that's all that matters