Nigel, read about DSS here:
Dynamic Soft Stabilization
There are several huge advantages of DSS over Dynesys. Location of pedicle screws for DSS is much less likely to result in broken screws... one of the more common complications with Dynesys. Also, the modular design allows combination soft stabilization / fusion procedures. So, the same system could be used for your fusion and soft stabilization. If things go bad for the top level, converting to a fusion would be removing only the soft stabilization module and replacing with fusion module. Same screws... same system. Also the control of motion with DSS is different. I should have more info after NASS next week.
Mark