Is it a good idea to convert a 192kbps stereo-ac3 to a 256kbps stereo-mp3? what is the equivalent mp3-bitrate for a 192 stereo-ac3?
Actually, 192kbps ac3 is equivalent to 160kbps MP3. But you can't talk about such terms here, because you're recompressing a 192kbps ac3 to mp3. So even 320kbps mp3 will be inferior in quality to the original 192kbps ac3.
keep original 192kbps ac3, or go to 90kbps ogg vorbis.
90kbps vorbis? thats not really much :p