While downward wage rigidity poses possible adjustment problems in Germany, it could well be that, like many other Western economies, Germany is producing more services while more of the world's manufacturing is being carried out in other lower-wage countries. I'm not sure this reaction to shifting comparative advantages is all bad. 

If I understood him right he said that the shifts from labour-intense sectors to more capital-intense sectors and from production sectors to service sectors were much too fast. With the current speed the shift is destroying much too many jobs, he claimed. According to him, the spectrum of wages should be opened to the down-side, meaning that more low-level jobs should be created.
Of course this would result in social tensions. He accounted for that with the concept of "Aktive Sozialhilfe" (active social support), meaning that people with low-level jobs should receive financial support from the state, in addition to their (low) wages.
The brilliant thing about this idea: it would cost less to the state compared to the actual costs of unemployment because employment rises then the state has more money.
Drawback: potential opportunistic behavior on the side of employers, meaning that they could pay low-level wages to ALL employees and thus place an additional burden on the state. 

Maybe Sinn should have emphasized more clearly (during his presentation) that by removing wage rigidities new low-level jobs would be created, i.e. that there is no chance of competing successfully in certain sectors but that there is demand for existing or new products/services if offered at a lower price. [After all, 90% of the questions in the Q&A session were closely related to the labour fallacy, the luddite fallacy and the "Keynesian demand fallacy"].

I think his theory is logically consistent and backed by empirical evidence so one should only haggle about the size of the effect...