Poor sound with an AV Receiver

Hi i recently bought the new Onkyo TX-NR1030 AV Receiver and the 5.1 THX (T3-5.1-UL) Crystal audio system as a Home Theater for my living room.
Besides from connecting a Bluray player, Xbox One, Ps3 and some other stuff, i have connected a brand new HTPC, with Windows 7 OS, i5 CPU, 8GB RAM, SSD etc
The problem that i have is while playing mkv movies, with DTS or even DTS-HD soundtracks, the sound volume is pretty low considering that it turned to 40-50 % of the total volume of the system!!
Are there any special settings that i have to make in the k-lite pack for the audio to be stronger?
The connection between the HTPC and the Onkyo is made through the AMD graphic card that i have installed, the 4870x2 which supports DTS-HD etc.

From your last sentence I deduce that you are using audio pass-through? In that case the decoding is done by the receiver and the receiver is also in control of the volume. It should have a "Night mode" or "Loudness Management" option somewhere that allows to reduce the dynamic range of the volume. Then speaking will be louder and explosions will be quieter.

To control volume with the HTPC you have to disable passthrough. Then you have the ability to use volume normalization, which is similar to the options mentioned above.