They are completely different beasts - the digitheatre is an all in one pack with amplification and DTS decoding, the Cin6Pack is a set of speakers and sub. Only the sub is amplified (active).
If you got the latter, you`d also need an amp, and unless your DVD player can decode DD and DTS, you`d need an amp with that facility. These start at around £200, so add that to the cost of the speakers.