I went from a Cat 4 and FO to Cat 6 alone. I didn't touch anything else, I re-ran all three hard lines in the house and shop. Cat 4 to Cat 6. 20, 50 and 100 foot runs.
It was like magic.. 15, 20, and 35.00 dollar cables. I had zero errors before and zero errors after but 10X increase in DL and 2 or 3 X in up load, bidirectional.
100.00 upgrade, 5X increase in overall speed.. YES the sound improved..the shop more so, (the longest run and Cat 4 only before). I like the CAT 6 connections too..
Regards