best suited development framework for special use audio player?

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cross-platform

I have a question regarding the most suitable development framework for an intended commercial project.
The main functionality would be to play one single .mp3 or .wav file hundreds of times simultaneously, with one instance at full volume and the others at lower volume.
We already looked into different options - using C# it does play a couple of hundred instances and uses not too much CPU and RAM resources, but the intention is to go multi platform - Windows/Linux 32/64 bit; Mac; if possible also Android and iOS.
As more features would be added later step by step, what would be the cross-platform development framework best suited for this?
JavaFX does not seem to be powerful enough - plays not enough tracks simultaneously even at 100% CPU; also has issues on Mac - at least with our trial implementation.
The focus would be on uninterrupted audio output with the lowest possible system resource usage.

It seems like Qt might be well suited for this project; or are there better options? wxWidgets?

For JavaFX there is the Scene Builder to create/ change the GUI in an easy manner while not touching the main code - the framework we look for should also have this option.