First nitpick, double NAT'ing is beyond kludgy and will cause issues, please don't double NAT. Think of the children.
Second nitpick, you have 3 gateway devices on your network, our goal should be to have only one. Once again, the children will thank you.
Now, on to the existing design. Do you realize that clients of the first DSR will have access to both networks unless you specifically start writing firewall rules? You normally route all networks (0.0.0.0/0) through a VPN, and that DSR itself has routes to both networks (and indeed everything not destined for the 192.168.0.0/24 will be NAT'ed from the DSR itself).
Given the above nugget I suspect you can see where I am headed, there is no reason to use transparent mode on the second DSR (and perhaps no reason for the second DSR at all), because all the VPN clients (of either DSR) are going to have access to it's WAN network and all it's routes anyhow. It's LAN network (which is presumably unconnected) effectively becomes a black hole network. And since we don't want to have to touch on adding routes to everybody on the 10.54.85.0/24 network for your VPN clients, this solution will be much cleaner.
Also, forwarding VPN traffic to multiple gateways is a little bit of a special trick depending on protocol and gateway, not something I would touch with a 10m pole by choice.
Please understand that I am only trying to help when I say that this design is going to be trouble for you, redundant hardware and NATs are going to cause issues, embrace appropriate GWs that can handle all of your needs (which could be the DSR, or the Sonicwall, or a 3rd option for all we know at this point) and appropriate LAN side segregation.
