Which makes me wonder how many people have tried 2 nics in a music server - 1 for access to the internet and 1 direct - connect to renderer versus connecting each component to a switch.
I wish there was an easy and simple answer to all these questions. I have done many of these tests myself and have some valuable information I can share, but it's never easy, because the answer is never Yes or No. Or good, better, worse.
Every time I see a question and want to jump on it to provide what I think would be valuable feedback, I realize I have to spend an hour to write an extensive answer that describes the different aspects of the problem. The main reason is that there are too many factors to consider with every change you make.
So without trying to answer this particular question, because I don't have an hour at the moment, I would give you a couple of pointers to think about. I'll do that in the form of questions that we should be asking ourselves and trying to answer when introducing a change like that.
- Will the two NICs be taking power from the motherboard, ot will they be powered by external power supply?
- If powered by the motherboard, wouldn't that pollute the power quality for the other components also taking power from the motherboard? Certainly as the NIC consumes power it generates some noise... how does that impact your overall sound quality?
- If powered separately, is there a way to isolate the ground? Or will the ground be common? If the ground is common, how do you prevent the noise that comes into one of the NIC to go to the other NIC or the rest of your system?
- Also if powered separately, what kind of power supply are you using? And how does that interact with the rest of your system?
- Could DC cables act like antennas? If yes, how adding another DC cable to power the additional NIC affects your system?
- Do Ethernet cables act like antennas? If they do, what happens with your system when you connect two Ethernet cables to your computer instead of one?
- Are you using the same NIC model or different? If different how does the second driver impact your computer?
- How is your OS impacted by having to deal with two NICs and how does that impact the sound quality?
- What is the overall impact on your computer sound quality by changing it from one NIC to two?
- Are you preventing some noise coming from your network by using two NICs? Or are you injecting twice more? Or somewhere in between?
All these questions are just touching the surface of what is happening at a micro level. I can easily dive deeper and provide 10 times more. And that would be all from a technical aspect not even taking into account personal preferences, musical taste, and your local environment. This is why some of those generic questions are difficult to answer. There is too much to consider, and it's very difficult to predict what the overall result would be.
On the other hand, there are things that are easy to recommend. For example, most home networks have a modem, router, firewall, WiFi access point, and a switch. ISPs often give you one device that can perform all 5 functions. You can think of this device as a surround receiver in HiFi. Those receivers are all-in-one devices too. They have a power amplifier, line stage, DAC, phono stage in some cases, etc. Chances are that replacing a cheap surround receiver with a good quality mono blocks, line stage, DAC, phono stage, etc would give you good results.
Well, the same way replacing the all-in-one ISP device with a good modem, a good router (i.e. Ubiquiti EdgeRouter), a good switch, etc. would give you better results for streaming. That's what makes this an easy recommendation. And when you do that, another easy recommendation would be to replace the cheap wall wart on each of those devices with a good power supply. And when you do that, another easy recommendation would be to replace the cheap $1 ethernet cables with better ones. But pay attention to what we are doing here - we are not really changing the design much. We are sticking to the design we have and upgrading the components. This eliminates the almost unlimited number of variables. As soon as you make a design change, we are back at the hundreds of questions we need to answer and not comparing apples to apples.
Just to be clear, I am not picking up on this particular question. It's a valid question. But I meant to post why some questions are difficult to answer.