I am not an expert on your machine but I had to run through a lot of things to get an HTPC I built (Lucid & XBMC based) to use HDMI, mainly by updating ALSA. Debian testing doesn’t need the updating though.
I apologise if this is too basic, but the fact that you had sound in VLC makes it appear that HDMI is working, but you are not outputting to it.
Here are a few suggestions from a non-expert:
1) Run "alsamixer" in a terminal, and check that your HDMI is recognised (alsamixer uses various function keys to operate, but has on screen instructions. I am on an XP computer here and can’t check). Possibly choose it as default.
2) Click on the sound icon to get the pulseaudio preferences and change the output to HDMI.
3) VLC and SMPlayer have options to change the sound output. I use SMPlayer, and in the preferences, if I set sound output to ALSA 0,3 (choose from a drop down list), I get the hdmi output. You can feel your way through the VLC menus to find the equivalent. This won’t help with the browser though.
If your problem is deeper than that, I won’t be able to help - but hopefully it is simpler than you think!