I suggest you look at C++ toolkits like juce or qt.
They both bring you crossplatform support out of the box and have a lot of the hard work done for you. It will make C++ much easier to handle too. Not at the “easy of coding” level of C# or java, because you still have to manage memory, but still.
Juce is especially suited for real time audio apps. It’s made by the guy who later on made tracktion IIRC.
Both are free of charge if you open source your app. (Qt is LGPL, so you could make a commercial packet with that one)