Iv got the HD-DVD box set of harry potter years 1-5

Picked up the bluray 1-6 box set

Im disappointed that the blu ray only has the last film as trueHD whereas the HD-DVD box set had them all as TrueHD, is this a bluray limitation?

There are no format limitations like that, its down to whatever audio stream theyve decided to put on the discs.

Maybe you should send it back since you have the HD-DVD set and wait for the all-encompassing Hogwarts Deluxe Phallerectus Maximus BD edition that will be out when theyve wrapped up Deathly Hallows.

Thats because Warner Bros supported the dead HD-DVD format so have never given the early films proper bluray treatment.

Dont they have DTS-MA on them?

DD EX is all they seem to have, the 6th film has TrueHD