Why do I need a switch?

@tonywinga So what I hear you saying, based on your description, is that you have Wi-Fi signal level issues that were remedied by hardwiring. I always recommend hardwiring backhauls from Mesh network nodes to avoid those exact issues. 

The differences between cable specs are all about supporting longer distances, higher speeds, and reducing RF noise pickup through known methods. Cat 5, 5e, 6 (tighter twist, shielded, 6a (higher spec Cat 6), and 7 (change to Gigagate 45 connectors). 

Luckily audio is a very low bandwidth network load, with few if any commercial offerings requiring more than 5Mbits/Sec (24-bit 192 KHz), well within the capability of even Cat 5'S 100Mbits/Sec @ 100M. If you were having issues it was likely RF interference related that the higher spec cable shielded from better than what was used before.

I you have adequate ports and are satisfied with your WiFi performance, you do not need a switch. No switch, regardless of their claims will make better zeros and improve your 1s. Those who make that claim are preying on the ignorance of their customers. Noise is the enemy of sound quality, certainly, but digital, or quantization noise occurs in the analog to digital conversion process as a function of accumulated rounding errors that result from mapping a near infinite dataset into a finite space, e.g. 16 bits deep sampled at 44.1 KHz (CDs). And that has nothing to do with the Layer 1 and Layer 2 data transmission that is Ethernet, wired or wireless. Other noise, from cheap power supplies or poor analog circuit noise rejection, for example do not exist in the digital realm unless they preexist in the input signal and are quantized in the ADC process. Again, nothing to do with Ethernet.