Hi,
First thing to realize is DVI means digital VIDEO interface....does not integrate sound into signal, and HDMI means high definition MULTIMEDIA interface...yup includes sound as well as video!
If a DVI out is all you have access to from your vid card/mobo, then a y splitter (2 inputs 1 out) 1 input dvi, 2nd input for your sound, output being HDMI may be difficult to find, although i am sure it is out there.
Alternatively, run a 2nd line alongside your DVI to HDMI line just for sound, or try to use a different output from your card that supports both video and sound if available. Most video cards these days have several outputs to choose from.
I suggest reading up on your specific card, and determine which output best suits your needs.
Hopes this helps with your issue!
Regards