Why are digital streaming equipment manufacturers refusing to answer me?

I have performed double blind tests with the most highly regarded brands of streamers and some hifi switches. None have made any difference to my system on files saved locally. I have asked the following question to the makers of such systems and almost all have responded with marketing nonsense. 
My system uses fiber optic cables. These go all the way to the dac (MSB). Thus no emi or rfi is arriving at the dac. On top of this, MSB allows me to check if I receive bit perfection files or not. I do. 
So I claim that: if your dac receives a bit perfect signal and it is connected via fiber optic, anything prior to the conversion to fiber optic (streamers, switches, their power supplies, cables etc) make absolutely no difference. Your signal can’t be improved by any of these expensive pieces of equipment. 
If anyone can help explain why this is incorrect I would greatly appreciate it. Dac makers mostly agree, makers of streamers have told me scientific things such as “our other customers can hear the difference” (after extensive double blind testing has resulted to no difference being perceived) and my favorite “bit perfect doesn’t exist, when you hear our equipment tou forget about electronics and love the music”!
Hi @mihalis yes, it’s the ProUSB / ProISL combo:


It’s the two part combo (scroll down on that link above):

  • Pro ISL Input Module
  • Pro ISL cable
  • Pro USB
That’s what I wrote on my previous post, no? Is this not what you meant?

Some really good points about A B which I will address here. Since someone attacked my person for some mysterious reason, I am forced to explain that these tests were always done with a group of experienced audiophiles in Asia and in Europe. To them we added some friends who aren’t audiophiles to make sure we don’t have any bias from that. We did double blind tests, not triple blind. The groups were not the same always. And the tests were two hour affairs on occasion and not some extensive lab test. I am claiming nothing other than what this meant for us. 
The post earlier about how the ear isn’t made to compare is I believe correct but our methodology probably eliminated this bias. 
First we listened with knowledge of what equipment we are hearing. Then we listened to equipment which was given a code (not A or B but eg 346 and 589). And finally we listened to unidentified equipment in random order and asked to identify which code it was. 
Various pieces of equipment had different success because many obviously do sound different. But with equipment which shouldn’t really make a difference according to some logic, we had the following results

1) consistently, expensive equipment was identified as better and we could all elaborate that we heard specific differences. I certainly did think so

2) consistently, when the equipment was labeled, we could not necessarily say if it was overall better or not than the other but we developed certain characteristics we each thought we heard. These characteristics were not consistent between each listener but the same for each listener

3) not one person was able to identify these differences with more than 20% consistency vs 1 or 2!!!

Take me out of the equation since I am apparently a troll. The people in these rooms are audiophiles with significant experience, from different cultures and of different ages. We were stunned. (Non audiophiles usually abandoned us after 30m).

What this meant for us? If we smell something doesn’t make sense, we look into it so that we don’t end up spending our savings towards the wrong equipment or system. Ie we try to reduce bias. As a result we feel we have better systems with less equipment and less cost. 
This is how this worked for us. I am sure everyone has their way and I am not making any broad généralisations about anyone else. I did feel validation when I read the seminal work of o toole and some sites which do measure equipment extensively with correlation to performance potential. 
To each their own, although I hope at least some of you may consider these points.

troll out!
Thyname you wrote feeding via usb and I wanted to be sure that the prousb conversion was involved. So if you know more about how your streamer would improve the signal it would be great to hear it. It goes against what msb and other steamer makers are saying but maybe there is something they are missing. I haven’t had the opportunity to listen to this steamer, looks terrific.

kijanki much appreciated. Exactly, I am focused on the fiber connection because it eliminates all electrical interference. What I struggle with is that since the signal is bit perfect and the fiber eliminates noise which would have affected the dac, wouldn’t we be getting data = what was sent? Thanks again, getting late here in Europe. 
Thyname thank you for the more extensive response which I hadn’t seen until now. Going for that bath now! M.
@mihalis I simply shared what I experienced, with that MSB DAC and that same module. Which MSB DAC did you own? I don’t see it under the System for your current gear. So for the ProISL / ProUSB module combo, was it the same you had? That’s what I had.

My subsequent attempt in technicality of the benefits of USB protocol in streaming (or lack thereof) was simply based on my limited technical knowledge. I don’t pretend to be fully able to explain everything I hear.

As for the MSB ProISL / ProISL implementation, yes, the main objective is to eliminate copper, therefore the electrical interference associated with it, by introducing fiber. But it’s not as simple as that. The first device, what they call ProUSB (the dongle that stays outside the DAC, on it’s own) converts USB to their proprietary ISL audio transmission via the fiber. Then the module that goes into the DAC, what they call the ProISL module, is the one that is directly connected to the DAC architecture. Basically copper USB cable to the ProUSB dongle input, then fiber optics cable from the ProUSB dongle output, to the ProISL module (attached to the DAC) input.

So it’s not as simple as fiber, and here you go, all problems solved magically. The conversion itself is perhaps just as important, as in theory can introduce other issues.

Further, many of the non-believers will tell you that any of that is not an issue at all, and any competent Topping China $50 DAC has all that built in, galvanical isolation and all, so totally unnecessary to go through fiber they will tell you. So here is that.