Which DVD-Audio player are you using, and how connected?
Again, like you discovered after three years to get DTS, it helps to know what player you are using so we cover all the bases/settings . In forums like this you really need to be much more specific and verbose in the information you include when asking about A/V systems and their capabilities. It would really help to know how your components are connected and the settings/cabling options you have already tried.
My gut feeling is you may be required to use multi-channel analog cables in order to be able to enjoy the more 'proprietary' DTS 96/24 via DVD-A. Even though it's a lossy format this still may be what HK implements in your case on the AVR 146. I'm not 100% certain however. Take a quick look at the table on p.21 of the user manual online here-