Motorola BSR 2k and Arris CM900 Multiple-VLAN

Hi, we are trying to make a little lab for testings and we got stock !!! PLZ HELP !!!

Here's what we would like to do...

The client connect to Wireless Access-point that VLAN TAG by SSID.
Ex.: SSID=Test1 and VLAN TAG 40
SSID=Test2 and VLAN TAG 50

The ethernet interface of that Wireless AP is connected behing the modem (Arris CM900).

The modem are linked to the BSR 2k via Coax cable and get their ip address (172.16.16.x/20) from our Server acting as a DHCP Server. We would also like to make the wireless client get their ip address from our Router DHCP.

The BSR 2k have ethernet 0/0 connected to our Router port #3 that have the VLAN's Interfaces.

When i connect the wireless AP directly behind that router port everything is working well...

Here's a little block of configuration of our BSR 2k configurations :

!
interface ethernet 0/0
ip address 10.21.208.138 255.255.255.0
no shutdown
bridge mode trunk
!
interface cable 0/0
ip address 172.16.16.1 255.255.240.0
cable helper-address 10.21.208.30 cable-modem
cable helper-address 10.21.208.30 host
cable dhcp-giaddr primary
no shutdown
!

show ip route command returd this:
C 10.21.208.0/24 is directly connected, ethernet 0/0
C 172.16.16.0/20 is directly connected, cable 0/0
S 192.168.1.0/24 [1/0] via 10.21.208.1, ethernet 0/0

Our Router configs are like this:
Port #3: 10.21.208.1/24 (no vlan tag)
Port #3 VIF VLAN 40: 10.21.240.1/22 (VLAN TAG 40)
Port #3 VIF VLAN 50: 10.23.1.1/24 (VLAN TAG 50)

The routes on the router is as follow :
set device "port3"
set dst 172.16.16.0 255.255.240.0
set gateway 10.21.208.138

Thanks,