Ok. I got you now... your double NAT'ing. So your cable modem also is a built in router/firewall(statefull packet inspection).
If the cable modem was just a modem, you'd be ok, but since your NAT'ing and then trying to NAT again at the Sonicwall, I see the issue your running into.
What you need to do is look for something in the cable modem called bridging. This will make the cable modem act as a modem only instead of a router/firewall. This will bridge/pass the x.x.x.193/29, or whatever subnet your part of as it could be larger, directly to the WAN interface of the Sonicwall. You then setup like I stated earlier. You might need to define your WAN port as DHCP initially so you can see what your gateway will be or if you can currently gleen that info from the modem (again your public IP addresses might actually be part of a large shared subnet and not just your own small subnet).
I mentioned the X1 and X0 interface as Sonicwall marks their ports (maybe not on that model, but all of their newer models) X0 default for LAN, X1 default for WAN... the GUI's designation of LAN, WAN, WWAN, OPT are more technically zones so security can be defined on what traffic is allowed to denied between zones. Those zones match up to physical ports and as stated, X0 defaults to LAN(zone) and X1 defaults to WAN(zone).
Hope that helps.