It would definitely help for some types of RFI, but not for others. Remember, the issue isn't something corrupting the digital stream (if that happened, you hear drop outs and pops...very very obvious problems) The issue is unwanted signal being injected into the DAC, usually impacting the ground plane. Remember, that in the D to A stage, the reference is the ground plane. If the ground plane is bouncing around, then there is a definite audible impact on the analog output
So in managing RFI, where are all the places that it can get injected into your DAC? Those are your soft spots. The DAC designers build in a lot of shielding and isolation for those soft spots, but stuff can still leak through.
For mScaler and a DAC, you work backwards from the DX inputs on the DAC: the cables can pick up ambient signal in the air (shielding can help here), the cables can be touching something (power cord, etc) and picking up some stray fields (shielding can help here), or the cables can be transmitting RF from the mScaler (shielding **won't** help here).
It is the last case where the ferrites made a huge difference. The mScaler is a pretty serious compute engine and is generating RF at particular frequencies. Some of that leaks through the BNC cables to the DAC.
Based on their geometry and the materials they are built from, the ferrites are basically dampeners for particular frequency ranges (think of them as filters). A lot of the early experiments with ferrites was looking for the frequencies that needed to be filtered out (turned out to be in the 2.5GHz range, IIRC) Putting these on the BNC cable basically absorbs the RF energy in this frequency range so it doesn't get to the sensitive DAC. More ferrites tuned to the frequencies you want to filter, the more you filter out. Eventually, you filter out so much that you can't hear the impact any more.
Now different ferrites dampen to different degrees at different frequency ranges. Even if a ferrite is a weak filter at some rogue frequency, enough of them and you can filter stuff out. As long as the core digital signal (384MHz) remains strong enough for the DAC to lock on to it, filter away. There is no value outside of that 384MHz signal. If the DAC loses its lock on that signal, you will hear it in a big way (its a cliff, not a gradual degradation).
Now it so happens that WiFi (and microwaves and a bunch of other wireless equipment) really hammers on the 2.4GHz band. Well shielded BNC cables would definitely help here (keep the cables from being an antennae), but they won't help with RF being generated in the mScaler itself.
As always, very very environment dependent. Ferrites (and BNC cables) are relatively cheap. For <$100, you can experiment with cables and ferrites and see what you hear (see my big Blu2 review linked below, where I documented my ferrite experiments...I included some links there). If you add ferrites and you don't hear a difference, that's awesome, you're all set. If you do, keep adding them until you don't any more.
RF is insidious though. Upstream from your mScaler is USB (and the computer behind it) and power supplies to both your DAC and the mScaler. These are all potential vectors for RF to leak into your DAC and impact SQ. When evaluating things upstream from your HMS, your reference (At least with respect to RF) should be against an optical input. When you get your usb to sound as good as optical, you’ve arrived.
