I don't know the DVD player - but are you getting dts 5.1? Or are you not getting dts at all? If the answer to 1 is I am getting dts, then the problem is either:
a. You have selected the wrong audio track in the DVD language menu. Most DVD's that carry a DD & dts track will default to the DD track. Go to the spoken language menu and manually select dts.
b. You have not swithed the surround back speaker on. In the speaker set up menu on the amp, scroll down until it says SB...switch this to "yes" (providing you have a sixth speaker). Then, in the custom menu, switch "SB" to either "auto" or "mtrx". switching to "auto" will allow the amp to detect the sorround back speaker itself, switching to "mtrx" will leave it switched on all the time.
If the answer is "I am not getting dts at all", then it's probably a player related problem, which I'm afraid I know nothing about...
BTW, I don't actually own this amp, but my local Sony centre were kind enough to photocopy an instruction manual for me as I am "in the market" for something to tie me over for a year. The thing is, I hope they don't think I'm going to buy one from them when it actually £70 cheaper and in stock from Unbeatable...!!