[Impact]

The whole philosophy behind control-showing responses to 2C opening is that opener knows the combined assets (in controls) of the hands and should be able to proceed by asking bids (see various styles but simple Romex ControlAskingBids & TrumpAskingBidss are fair).

Whether you think control-showing responses are good or bad, it is unfair to evaluate them without a complementary set of agreements (and relatively stupid IMHO to play them if you do not adopt asking bid structures by 2C opener for suit play when agreeing trumps).

In this instance over the 5+S showing bid a 4NT TAB in S would be a good start - or alternatively as Phil suggested a 5C to ask as CAB - so that if he denies the CK you know he has the DK and can then TAB with 5NT for the grand.

As Mikeh indicated, the 4D bid creates problems rather than solving them...

regards,