Media Player Classic is primarily a video playback program. Foobar2000 (and other like programs) are designed for audio. basically I think you will find Foobar2000 (and the like) is better suited for audio playback than Media Player Classic is as it’s interface is nothing fancy but the program does what it does well which is playing audio and you can even open different tabs and load up whatever music files you want in them by dragging and dropping audio files in there etc and converting files, once you do some basic setup, is pretty easy to.
but any .WAV files you currently have can be converted quickly to .FLAC as there is zero reason to keep .WAV files since they take up about twice the storage space with zero benefit over .FLAC as there is no loss of sound quality converting a original .WAV file to .FLAC since it’s a lossless audio format. so basically .FLAC outright tops .WAV because it takes less storage space for identical sound quality.
but if your ever low on storage space for mobile stuff etc… Opus is likely what you want (assuming your device can play these files) since it’s the most advanced lossy audio format right now as depending on what kind of sound quality your happy with you can lower the bit rate quite a bit with Opus and still have decent sound quality as even 32kbps or 48kbps, which is quite a low bit rate for music, still sounds alright considering the very low bit rate. but, in my opinion, I would generally choose either 64kbps, 96kbps(I suggest this as a default for most people since I think it’s the sweet spot in terms of sound quality/file size), 128kbps as a general guideline as you will probably find one of those three settings to suit your needs and they are still efficient to as much beyond 128kbps with Opus is a waste of storage space with minimal benefit as efficiency starts to go out-the-window much over 128kbps.
but when it comes to speech with Opus v1.3… I find down to 13kbps is quite good overall in that sound quality is still decent (especially if your source file has good sound quality to begin with) but file size is kept VERY low. in my opinion, I would generally avoid going any lower than 13kbps for speech (and one might prefer a bit higher if you want to play it a bit safer) with Opus v1.3. but for the previous release of Opus, which is v1.2.1, I would suggest no lower than 14kbps. but if you want sound quality pretty close to the source file then you will have to bump up the bit rate a bit. but since it’s just speech I tend not to be as picky as I would be with music.
just some thoughts. have a good day