Multicasting - different subnets

I am trying to do multicast imaging through a layer 3 switch and different
IP subnets. The imaging server is in one subnet and the clients are in
another. The layer 3 switch is a Cisco gig switch that routes our LAN/MAN
traffic between several different subnets.

Main imaging server with PXE: 10.1.1.1
Clients are in subnet: 10.8.8.0
PXE and DHCP server: 10.8.8.30

In the PDHCP.ini file on the 10.8.8.30 server, I have the following set:
TRANSACTION_SERVER_IP=10.1.1.1
TFTP_SERVER_IP=10.1.1.1

The clients in this subnet get their IP number from 10.8.8.30, but then
download everything else from 10.1.1.1. This works great for unicast
imaging. I can set a machine to image, pull down an image manually after
booting through PXE, everthing is great. Except multicasting...When I
setup a multicast session in ConsoleOne the clients boot up, pull an IP,
load the imaging engine and join the multicast session only they do not
display a session ID on the screen. They just say waiting for multicast
session to start. They display the multicast address, but they will never
do anything. When I look at the imaging server screen it shows 0 of x
clients. Is there something I can set on the L3 switch to let
multicasting work. Multicasting works fine for clients on the 10.1.1.0
subnet.

Thanks,

B.J.