Thank you so much for alerting me to the fact that the frequency of the station must be the same as the GW1000 and for the fact that Froggit DP1500 is the same as GW1000. In fact my WH2650 is a 868Mhz station and I can easily order a Froggit DP1500 868MHz from amazon.de (around $55) or a complete package consisting of DP1500 + temp/humid sensor Dp50 + WH4000SE station for around $160
I am going to wait a while to see if Mark comes up with a solution for the WH2650 to connect directly to CMX, but if this connection is not possible, then I will go for the DP1500. Once again, thanks for this precious tip.