Tvheadend cwc client only works with cardservers that support the newcamd protocol. The creators of cccam decided to only implement the newcamd protocol when cccam acts as the client
So tat is why you can not connect to a cccam server with tvheadend. There are also no plans to include the closed source cccam protocol into tvheadend.
So this leaves you with the following options :
1) switch your dreambox to oscam and the connect directly to that from tvheaded
2) use oscam as a proxy to convert newcamd to cccam protocol
I hope this explains the situtation
Hein