About disabling IGMP Snooping..

[simoncn]

If everything is working OK for you at present, I suggest you leave your current settings unchanged.

IGMP snooping monitors responses to IGMP query messages for a multicast group. These messages are sent by an IGMP querier. A device that does not respond to IGMP query messages is marked as inactive (or not interested in messages for this multicast group) and will not receive subsequent multicast messages for the multicast group. This filtering could occur at any level in the network.

This mechanism is intended to prevent devices and the network from being flooded by some types of high-volume multicast messages that they don't want to receive (notably IPTV) while allowing these messages to be received by devices that need them. It is not needed for UPnP discovery messages because these are sent in compatively low volumes.