developing short SOX (sound exchange) script

I need very simple tool based on script. You have to add gui and one main feature to it. I have S0X based script which does a few things:. - combines each of source wav files put in particulair dir (lets call them source files) with another wav file which is one fixed file (lets call it fixed file). - it converts format, it changes names it, saves dest files in destination folder Has ca 30 lines, it works perfect. What i need to be done: - Simple GUI Interface (select source folder, select dest folder + some volume settings for both source and dest files, set default combine ratio) - And the main feature to be done: automatic changing and setting the volume of fixed file while combining / mixing it with a source file. So the script should know what is the dynamic of the source file (don't know how, it may be RMS, volume or other readable parameters concerning dynamics which are available in s ox) and thus set the volume of fixed file to sound as both files are on similar level, combined in the destanation file So then if you have any fixed file and want to combine it with other source file it's no matter if the source file is very loud or very silent as this tool should increase or decrease volume of the fixed file. Notice: - Source file may contain loud or silent parts (it's music) so volume of fixed file being combined should base on current 'volume' level of source file - When I say volume it also means volume and dynamics as volume is not enough informations. Dynamics can be read in sox from file afaik.