Cable vs fiber for audio quality

I wouldn't worry about it. Besides, it's going to be on and in use 24/7 from the moment it is installed, so any theoretical burn-in benefits will take care of themselves pretty quickly.

Q modem “ burn-in” ?
A: nada … not an issue .,,, there was no run-in time on my new modem required from this last week . ( I use “ run-in” instead of “ burn-in’ as a better and more accurate representation of initial use )

If it’s irritating “ brightness” you seek to tame , here’s a list of the sequential journey of what did it for me. I’ve got a high-end streamer/DAC in a high-end 2-channel system . Certain add-on units and tweaks provided necessary audio performance improvements that took everything to the next level

- No change in the modem or the internet provide platform (copper line vs cable vs fibre optical ) had any noticeable impact to me.

Ethernet cables matter. Think high-end silver over copper quality build high-end Ethernet CAT7 cables, with Telegartner connectors. They smoked the run of the mill budget stuff . They DO matter. Think AVANTI AUDIO as what worked for me that bested too AUDIOQUEST in my system and at half the latter price . The digital glare and sibilance was significantly suppressed .
 

Read on

- next …. NETWORK SWITCH & LINEAR POWER SUPPLY:  .,,,, think Silent Angel audiophile network switch with an external quality build linear power supply add-on. I was a big skeptic and a non-believer too,  until I got one and I was surprised how much this duo further

- lowered the background noise and

- further tamed that digitsl “ brightness” “edge” and “glare”.

- YOUR STREAMING EQUIPMENT; $300 does not compete with $3000+ Build quality in both the high-end streamer and its stablemate high-end DAC matters big-time ….. full stop. The brightness / glare etc is progressively suppressed as you go up the food chain, If you need a litmus test, go toddle down to your bricks and Morse store and sequentially audition a bakeoff between sub $300 option against a then against a $$3K -  5K strata option.

- Digital recordings resolution and its bespoke mastering is a wide range outcome option, Think : /192 digital recordings over 16/44.1 in general whenever possible. if properly mastered , top hi-rez are another material step up from 16/44.1 cd rez files.
Depending on the recordings , they can compete with the performance of my very high-end REGA ISIS VALVE cdp/ DAC , and are true contenders and no pretenders

- STREAMING SERVICE PROVIDER : QUBUZ bested TIDAL in my system ….go figger. Who knew?

Unless you are streaming at the highest levels, and you equipment is at SOTA levels, I wouldn't be concerned about the differences between fiber and cable.

B

I don't think there's going to be any audible difference at all.  The quality will depend on your streamer.

Having said that, reliable is better than not.  My normal cable provider is fast/cheap and sometimes goes out for days at a time, so I also have T-mobile as a hot backup for work reasons.  Except in the middle of failover I never even notice the change has happened.  What I do notice is that I no longer have long stretches of time when my Internet is down.