I've just had this combination on my 156 for 50,000 miles and to be honest, although the car handled OK I never really felt like the FSDs were working properly with the Eibachs.
The Konis are now completely knackered and speaking to a couple of suppliers, the FSDs aren't really meant to go with lowering springs, the lowering takes them 'out of their range'. The early failure of the FSDs makes me think that maybe this has led to their relatively early demise?
I've now sourced a set of Eibach Prokit dampers (meant to go with Eibach Prokit springs) and am having them fitted on Monday - I'll report back! Got them for £300, pretty pleased about that but only if they work well of course!