The r8125 works for me at DSM 6.2.3, however I can't get the hard disks to spin down, no matter what I try (using tmpfs for several mounts, disabling logs and all possible services).
I was happy with DSM 6.1-15101 Update 4 for several years and it was the last version that I had no problems with hard disk spinning down after selected time of no activity.
I was able to compile r8125.ko for DSM 6.1-15101, however it doesn't load (error: "region #1 not an MMIO resource", reported for other realtek adapters and different systems too).
@IG-88
What driver source did you use for r8125?