I did some struggling on this for my Hauppauge PVR-350 as well.
There is no support for channel tuning in the Dvideo interface on VLC yet.
However if you can manage some kind of out-of-band channel to your streaming box then you can probably come up golden.
In my case channel tuning is performed using a tray app that comes on the card CD. This app is gettings it's shiny buttons stroked by a Girder script (
http://www.girder.nl)
That script can be called in any number of ways - like IR remote for instance, but I settle for command line since then I can call it using perl scripts and stuff.
Girder also has a TCP plugin that enables it to listen to commands over the internet, I have not yet looked into this but it seems pretty powerful.
Maybe too powerful
Cheers!