Why does headset work with other apps but they doesn't with voice chat?

[MathewShadowsong]

Okay I've been looking around for an answer:

https://community.secondlife.com/forums/topic/101076-sl-voice-not-working/
https://community.secondlife.com/forums/topic/420814-sl-voice-help/
https://community.secondlife.com/forums/topic/411510-voice-not-working-done-everything-in-support/
https://community.secondlife.com/forums/topic/321638-how-can-i-fix-my-sl-voice-it-no-longer-works/
https://community.secondlife.com/forums/topic/418383-there-is-a-problem-with-my-sl-voice/

As you see, seems that there is a lot of people with the same problem.
I think, I've tried all the solutions they suggest above, without result, all except that one of locked ports by ISP.
I've thought it might be a trouble of compatibility with some headset devices, brands, models, etc. I don't know, perhaps any conflict with the slvoice app which allows you to use voice chat. This use to happen with some videogames.
I say this because most of the people with the same problem report their headsets work with other windows apps, but they don't work with slvoice.exe
So I left this here, waiting for any lucky solution anyone could suggest. Thanks.

Using Win7 Pro, last version of Firestorm viewer.