Source Specific sound issue

First off let me say I'm really pleased with Eden.

Now I have something of a strange problem regarding audio. I have installed on Acer Revo 3610 and all works fine Except there is no audio on any of the files in my movie subcatagory. The files are stored on a NAS device in a subfolder and the existance and details of the files show up fine, however, when i try to play them I get a minute "blip" noice, then silence.
My TV programs, which are stored in a seperate sub-folder on the same device work without issue, as do music items and youtube via the add-on

Additional - I have now discovered that the problem also occurs in MKV format TV shows, small "blip" sound followed by silence. Do I need additional codecs for MKV?

2nd additonal, I have movies stored in a couple of different formats, in one case I have an .avi of movie x AND the VTS (dvd format) files as ripped from the disk of the same movie. I get sound from the avi but not the other

Last edit, and boy do I feel foolish. Needed to un-tick the boxes that said AC3 capable receiver and DTS capable receiver. Now works a charm