The verdict

CPU
Beelink SER9 has 2.6x the CPU throughput (34,991 vs 13,700 PassMark).
Plex
Ugreen NASync DXP6800 Pro transcodes more 4K HDR streams (~8 vs ~5).
Idle power
Beelink SER9 idles lower (8W vs 24W) - cheaper to run 24/7.
Networking
Ugreen NASync DXP6800 Pro has more NICs (2 vs 1) - better for a firewall or VLAN trunk.
RAM ceiling
Ugreen NASync DXP6800 Pro takes more RAM (64GB vs 32GB).

Which wins for each job

Job Beelink SER9 Ugreen NASync DXP6800 Pro
Plex / Jellyfin ~5 streams ~8 streams win
Frigate NVR add a detector ~6 cameras win
Proxmox / VMs 34,991 PassMark win 13,700 PassMark
Firewall / router 1 NICs 2 NICs win
Local AI / LLM no slot no slot

Approximate - capacity estimates from curated specs, the same logic as the recommender. Verify against your exact setup. Prices move; check the retailer.

Full specs

Spec Beelink SER9 Ugreen NASync DXP6800 Pro
Price (list) $999 $1,099
CPU AMD Ryzen AI 9 HX 370 Intel Core i5-1235U
Cores / threads 12 10
PassMark 34,991 13,700
iGPU Radeon 890M (RDNA3.5) Iris Xe (80 EU)
NICs 1 2
NIC model Intel I226-V Marvell AQC113 10GbE
RAM max (GB) 32 64
M.2 free 1 2
PCIe slot none none
Idle (W) 8 24
TDP (W) 65 15