Using a fixed size pointer in Unity C# with a C++ external function

I am porting a synthesis language written in C++ into Unity as a dylib. The function that writes in audio takes in a pointer and then writes the samples onto the buffer.

     [DllImport ("librtcmix_embedded")]
     unsafe private static extern int RTcmix_runAudio(void* k, void *outAudioBuffer, int nframes);

The outAudioBuffer is the pointer to where the samples should be written and nframes is the buffersize. Ideally I'd like to give this function a pointer and take all the resulting samples and write them onto the data[] of OnAudioFilterRead. OnAudioFilterRead has a buffer of 2048, but I'm really not sure of how to either feed the externed function a properly sized pointer or access the new information in order to write to data[]. Attempts to do this with fixed and various structs have just crashed unity. Here's my current crashing code.

     unsafe struct FixedBufferExample
         {
           public fixed int _buffer[2048]; // This is a fixed buffer.
         }
 
         void OnAudioFilterRead(float[] data, int channels)
     {
         unsafe{
             fixed (int* buffer = _fixedBufferExample._buffer)
             {
                 RTcmix_runAudio (null, buffer, 2048);
                 for(int i = 0; i<2048; i++){
                     data[i] = (float) buffer[i];
                 }
             }
         }
     }

What I'd really like is something along the lines of:

     void OnAudioFilterRead(float[] data, int channels)
     {
                 int *buffer = malloc(2048);
                 RTcmix_runAudio (null, buffer, 2048);
                 for(int i = 0; i<2048; i++){
                     data[i] = (float) buffer[i];
                 }
     }

Any suggestions for how to deal with these pointers?