Prosafe M4100-50G-POE+ and Multicast between VLANs

I am using an M4100-50G switch and am having problems getting Chromecast devices to work properly if at all over VLANs.

Several VLANs are configured and 4 x Prosafe WAC730 access points are providing corporate, BYOD and guest wireless networks. A seperate WLAN is configured for a few Chromecast devices.

A Sonicwall NSA 2600 firewall is providing internet access and dedicated DHCP, DNS and RADIUS servers are in use as opposed to using on device services provided by the switch or firewall.

Things work pretty well but we have really struggled with the Chromecasts. They connect to the internet but cannot be discovered by devices in the corporate WLAN which is the required result.

IGMP snooping and MVR have been configured a few different ways on the switch, but this has not really had any effect. If we enable multicast on the Sonicwall and enable mulitcast support on the interface/virtual interfaces that are used to provide internet access to the WLANs, the network floods rapidly and the Sonicwall admin interface becomes unusable until that physical interface is disconnected.

I am by no means a Sonicwall expert (or fan) and feel like I'm probably missing something pretty basic that I have just overlooked. The documentation for the M4100 is also not really that good and erroneous in many places as well which does not help.

If anyone could offer any suggestions I would really appreciate it.