Do upgraded LAN cables/purifiers/switch box make a difference. What is recommended, if so?

The answer is Yes. Check out Silent Angel.  They have some really great products and would further educvate you on the possibilities of sound improvement.  I understand that some of these options may be above your range.

Just to circle back, I agree with others to focus on the DAC first before tweaks (although the $40 NetGear switch isn’t too painful to try), and the streamer would likely make a significant improvement as well.  Not sure what your power situation is, but if you’re concerned with a lower noise floor you should budget for a good power conditioner as that will benefit your entire system and not just the digital side.  This one has gotten some really nice feedback from people here and is relatively not too expensive — just something else to consider FWIW.

https://www.kinki-studio.com/product-page/kinki-studio-x-vinshine-audio-tai-hang

I bought a trendnet 8 port unmanaged 1g switch for around $20 on amazon and I was surprised not only by it not harming the anything but it actually reduced a bit of noise. More natural sound. I have nice Ethernet cables and yes they make a difference. 

I introduced the LHY SW-8 and noticed slight improvements at best. It did seem to darken the background a bit. Worth the $? For me yes. But by far the biggest improvement was adding the DENAFRIPS Hermes DDC which I connected to my Pontus II 12th via I2S. What a difference!

Focus on the DAC and Streamer. The other stuff has never been proven to make a sonic difference. Some will say that it does. Please show me a statistically relevant test that some cable or wire sounds better? Save your money--Spend it on your kids.

Cheers,