Multicast ingestion FX2 chassis

I have got 4x FX2 chassis with FN410T IOMs. These are connected via network cables to a Cisco 3850 stack. The problem i have is that i dont understand Multicast enough (i know its a bit of a dark art), but my FX2 chassis do not seem to receive multicast traffic.

i have also got 4x AX740 S2D nodes and they, currently, appear to be working fine with multicast traffic, in both ingestion and distribution.

my Cisco stack has been working fine with Pim sparse-dense mode, and i dont believe i have got any rendezvous points for multicast traffic that has been initiated from within my network.
i have changed one of my FX2 FN410T IOMs into Full Switch mode so that i have got control over it, and have brought it back to a working scenario, albeit with an LACP trunk from the cisco stack to an LACP trunk on the FN to getting my main vlan untagged.

ive enabled ip multicast-routing, but this is where i start to get confused.

do i need to add RPs to my cisco stack? if i do that will i start having issues with my clients that also ingest this multicast traffic? should i revert my FX2 network back to Standalone, and it should just work?

any help would be most appreciative