Your question is not entirely clear to me, so my answer may not be exactly what you want.
MP3 files usually contain two audio channels, Left and Right, and “Joint Stereo” is the normal and best way of encoding an mp3 file using the LAME encoder. Other encoders may be different in this regard.
When using Joint Stereo, the Left and Right channels are transformed so that one channel contains Â½(L+R) and the other contains Â½(L-R). The first (mono) channel contains most of the sound information and is encoded with more than half of the available bitrate, and the second (stereo information) channel is encoded with less than half the available bitrate.
This results in slightly better sound quality than just using the “Stereo” encoding which allocates the same bitrate to each channel separately.
When Joint Stereo is decoded during playback, it’s simply a matter of calculating Left = Â½(L+R) + Â½(L-R) and Right = Â½(L+R) - Â½(L-R). So the stereo information is preserved as it should be!
Unless you really know what you’re doing and have a very specific reason for wanting “Stereo” instead of “Joint Stereo” in your MP3 files, you should just leave this at the standard setting (Joint Stereo)!
Every time you re-encode something that is in a lossy format such as mp3 into another lossy format (a.k.a. transcoding) you will lose some sound quality - this is completely unavoidable.
If you’re lucky and operating at very high bitrates, you may not be able to hear the deterioration in sound quality but it’s there.
I would recommend against transcoding your 192 kbit/s Joint Stereo mp3 files.
I don’t understand what you mean by “scraming”?
I don’t know much about the mp3pro format, so I may not be able to help you there other than saying, that my comments about sound degradation when transcoding between formats will also apply in this case.