If you want to use the same port as the old one, you need to remove the VLAN 600 tagging in router settings. New box is using Internet, no more special IPTV port. Alternatively, follow jusbella's advice above.

Will compete with Internet download. So far for years I used a router with good QoS and download does not affect Netflix, YouTube, Unifi TV or other streaming. When I do download or speedtest while streaming video, the download or speedtest speed will drop and give way to the streaming when it loads the next chunk of content. If not using router with good QoS then I guess the video quality will drop or playback will lag when downloading, unless TM have some QoS somewhere.

Or just use a router that can do both QoS and acceleration.

By the way, are you sure it does not apply to IPv6? From what I know, only the name is "NAT Acceleration" but it is actually more like routing acceleration. For some routers, it is known as Cut Through Forwarding, Fastpath, Packet Runner, Flow Acceleration or Flow Cache and only affects traditional QoS.