I'm not sure what the EWS3 chip is, but I'm 99% sure the EWS4 one is just a LIN-bus transceiver. This one specifically: E910.15 pdf, E910.15 description, E910.15 datasheets, E910.15 view ::: ALLDATASHEET :::If you look at the PIB in ISTA of the two cars (E9x vs E6x), there are two lines from the CAS on both. One is the start line and the other the comms line. The comms line goes to a different pin between mss65 and mss60, so tracing that pin on the DME back to the chip, continuity stops at an empty pad for either one respectively.
EWS3 on mss65:
Empty pad on mss65 (next to the upper 3140.3) where EWS4 would be
EWS4 on mss60:
Empty pad on mss60 where EWS3 chip would be:
Not impossible to solder them in, but not much luck finding datasheets on them.
EWS4 can fall back to CAN anyway, so not soldering that shouldn't be an issue. It's the other 30 components that might be a problem
Edit: This seems to be the "EWS3" IC: http://www.st.com/content/ccc/resource/technical/document/datasheet/de/4c/b3/3d/64/7d/48/8e/CD00001660.pdf/files/CD00001660.pdf/jcr:content/translations/en.CD00001660.pdf
I think it takes the EWS signal and converts it to a TTL signal so the DME can understand it. I believe the communication is unidirectional, which is why the modules have to be synced for starts to occur properly. EWS4 is bidirectional, so it needs a LIN/K-bus protocol. Advantage is no synchronization necessary - as long as the SK matches, the DME and CAS will figure things out.