Cisco WAN :: Routing With ASA 5505 WAN Via ADSL Bridge?

I'm trying to configure an ASA5505 behind an ADSL modem/router in bridge mode.The problem is the routing on the WAN side, because the gateway/next hop is a wierd address on the 10.x.x.x. range, outside the subnet.
 
So, I've got bridge mode working fine. If I take a laptop and configure it's ethernet adapter as the ADSL public IP with the wierd default gateway of 10.20.20.224 - windows complains about the gateway being outside the interface subnet but allows me to apply it, and it works, the laptop routes out to the internet fine with it's interface on the ADSL IP address.
 
So the bridging would appear to be working fine, negotiating the PPPoE ADSLand routing that transparently to the ethernet ports.But when I plug the ASA into that port and configure the ASA interface on the ADSL IP, I can't get it to route out properly.
 
interface Vlan11
nameif outside
security-level 0
ip address 60.x.x.151 255.255.255.0
 route outside 0.0.0.0 0.0.0.0 10.20.20.224 1
 
With the ASA in this configuration I can't even ping from the ASA on the outside interface to 10.20.20.224 and get a reply. With a PC running Windows plugged into the same port on the same IP and the same gateway, I can ping it (and route out) just fine.
 
When in bridge mode the ADSL modem/router assigns a managament IP to the ethernet interfaces of 192.168.1.1, so you can still connect to the device to manage it. If I change the 'outside' address of the ASA to 192.168.1.100/24 I can then ping to 192.168.1.1 and get replies, so the physical connection is fine.What am I missing here?