Oh, and by the way - I've written a small mixer application that works "almost" like the Shoutcast Source DSP plug-in (you still need it to broadcast, of course).
The program features all four sliders for regulating volume, and a push-button to start and stop talking (doesn't stick though, so click-to-start and click-to-stop). The main difference is - it lists all devices in the system, and all playback pins (with volume regulation) they have, and allow the user to choose which one he wants for music, and which one for microphone input.
Procedure: select the pin, click on Lock ('Zablokuj', EN version coming soon). Repeat for second source. Once both are Locked, the regulation and talk-button become active, and the program is in control of the mixer(s).
This also allows to regulate two inputs from SEPARATE sound cards, so if that's what You need, there it is!
For now the app doesn't remember its settings, but I plan to expand on that (remember selected devices, slider settings etc.).
For now, the download link is http://DevTEAMSoft.pl/CustomMixer.zip (about 677KiB).
If You find it useful, reply in this thread. I'm absolutely positive that it works - both for me, and for my friend that has a Realtek HD Audio card and now can freely select 'Rear Pink In' as the second source
I've also completed a new version of the .dll I'm using to handle more than two mixers at a time (the first version was really nothing more than a hack, to be honest), so if there's a need to somehow volume-mix more than one output, I'm listening... ;-)