WAV to MP3 conversion - then delete old WAV file

Currently a WAV music file is uploaded via the site and is saved in a folder called files_folder. Upon uploading a copy of this file is created and then mixed with another WAV audio file that serves as an audio watermark. This MIXED wav file is saved in a different folder called demo_folder - which is used for previewing music files online. This whole process is automated using SOX. Now I need someone to take the mixed wav file (that was saved in demo_folder), and convert it to high quality (320kbps) mp3 format. This new mp3 file needs to be saved to the same demo_folder and then the old mixed wav file needs to be deleted from the demo_folder. You will be given root access on the VPS server in order to complete this project so. With regards to software being used, because I've moved to a new vps server, SOX needs to be re-installed. Any other software you will be using (i.e. LAME, FFMPEG...) you need to install as well. With regards to the file names stored, currently the mixed wav file gets stored as "[login to view URL]" in the database, and this text also shows inside the product inside Joomla administrator. So the filename of files uploaded should stay exactly the same, just with the new extension of .mp3 and not .wav, so all the fields relating to the product that is created should be updated with new extension. The reason I dont want to just convert straight from original to mp3 while mixing is because this will result in too low quality preview music files. That is why I first do the mixing in sox and stay with wav format, only after mixing very hiqh quality files do i wish to convert to MP3. Please also ensure that the current player is compatible with playing mp3 files, BEFORE starting with this project.