DVB-T2 defines an optional MISO processing in its transmission chain to increase the diversity of the system with linear decoding methods such as ZF and MMSE. In this paper we propose to adapt the decoding process to choose between the simple low performance ZF decoder for non-frequency selective channels and an Adaptive K-Best Sphere Decoder (AKBSD) for frequency selective channels. We propose CIR-based AKBSD with some more complexity but enhanced performance. The adaptation process exploit the Channel Impulse Response to measure the channel selectivity and switch the decoding process between the ZF decoder and the KBSD with adaptive K paths chosen based on the selectivity of the channel. The BER and complexity simulations show suitable performance approaching ML for the AKBSD with acceptable complexity. The Adaptive Control Unit is implemented using VHDL and the overhead to the implementation of the regular K-Best SD is estimated.