BR500 routers and IPTV with lagging picture (Telekom) - reposted

I used to run a speedport Smart Router with Telekom Media Recivers (1x 401, 3x 201), not many specific options around but working fine.

Now using the Speedport as DSL Modem -> BR500 -> GS728 -> Clients

All Insight managed, all firmware up to date, TV picture freezes after 5-10 sec, even if just running one MR401.

Activated IGMP Snooping for the router and for VLAN1 (in use for all clients) on the GS728 - result: still lagging TV picture

Trying to solve:

1. Separate Media receiver clients into VLAN 4089 which is proposed for video - Media Receiver don't get IP adress anymore even though DHCP in LAN2/Port 2 is enabled on BR500

Hotine tells: IPTV and VLANs not possible on BR500 at the same time

IPTV VLAN 7 is needed to receive Internet from Telekom

2. Turn MR ports back to VLAN1 and try to set further multicast options on GS728 - no options available in Insight, just turn on/off

Hotline tells: take the GS728 away from Insight and manage locally

Further they have no clue what to do with Telekom Multicast in my ticket, but I've seen some descritions with similar issues here in the community.

Ok, turned to local web interface and try&error with hotline through the Multicast settings. Up to now this a very poor result.

Will try to add some screen attachments here.