Sometimes more is not better -or- Ethernet Overkill

I recently replaced my 30' Cat 6 cable with a pair of TP Link fiber converters, ended with a Cat 8 cable to my streamer. This was a good upgrade for sure, however I started to notice haze and grain in vocals after I installed a new digital cable between my streamer and DAC. The digital cable was an improvement in resolution, which probably made the problem more obvious, but not yet critical. I recently replaced the Cat 6 links between router/modem and router/FMC with a pair of Cat 8 cables. Everything took another slight step down.

I then replaced all three of the Cat 8 links with the original Cat 6, and my system is back to exceptional clarity.

Some relevant details on cabling, all the Cat 6 is tested Blue Jeans cable. The Cat 8 from the FMC to the streamer was a Linkup (https://www.amazon.com/LINKUP-Ethernet-Screened-2000Mhz-Structure/dp/B07VVFB8VX?th=1), the other two Cat 8's used on the router end were low cost (https://www.amazon.com/dp/B08PL1P53C?psc=1&ref=ppx_yo2ov_dt_b_product_details).

Yes, it could be the quality of the cable, though the LinkUp cable is no slouch. However, I also think that it could have to do with the extra shielding on Cat 8, and the connection that shield makes between the devices. Could this be acting as a channel for noise into the router and FMC's?

Anyway, thought it worth sharing. Try swapping out those Cat 8's for some quality Cat 6 and see if you hear a difference.