Hi,
In best case I would like to do:
Get voice from PDA build in microphone, output to headphone; switch it to (mono) Bluetooth headphone (not using its microphone). It would be great to use equalizer too.
Recording is not necessary.

It sounds easy but I didn't find any solution at the web.
StompBox.exe is the only application with the nearest solution. (just show me it's not impossible at all) But finally it's overloaded and changes the voice. And switching to Bluetooth i.e. with BTaudio/ BTmusic will also switch to the Bluetooth headphone build in mice.
The solution may solve two things, first think about hearing aid and second it could be a trick to send build-in FM Radio sound to Bluetooth Headphones. (need's a hardware change too)
(It seems that Mobile FM Radios are hardware wired to headphone/ speaker and can't be controlled by software)

May be I can find a programmer here to talk about how it can work or why it seems to be impossible.

Regards