To be clear, I never doubted Andy 
It’s TP-LINK’s support that I doubted, and with reason. Now I’ve got another reply from the english support team.
Their answer:
“Dear Wouter,
Thank you very much for your email requesting information about our product. This is Austin from TP-LINK support group.
On the latest firmware of TL-WR1043ND, there is no option for you to turn on or off IGMP multicast, but it supports this feature. Generally, IPTV users requires this feature on the router, if you have IPTV service, then you can check the IGMP multicast by IPTV.
For any further help, please feel free to let me know. To get technical support more quickly, please go to https://www.tp-link.com/en/support/faq.aspx?type=2
Best Regards
Austin Hu
Technical Support Engineer
TP-LINK TECHNOLOGIES CO., LTD.”
UPDATE 16/02/2011
And I received another mail that confirms again:
TPLINK TL-WR1043ND router supports IGMP v1 and v2.
So it seems compliant to A&H requirements for multicast.
Wouter
My prayers have been heard, Dante is coming!
