Help needed getting MP3 OutputMixer working on A1S AudioKit

[level0dev]

I'm trying to play two MP3 at the same time using an OutputMixer, but no matter what, my playback is too fast AND I get messages of insufficient buffer.

I tried increasing the buffer in minxer.begin() but while the speed might be changing slightly (it's hard to know for sure, the playback is still way to fast) I keep getting buffer increase messages in the serial monitor.

I tried running the mixer with only a single file (OutputMixer<int16_t> mixer(i2s, 1); and all mentions of audio [2] commented out) - it plays slower than when I try to play two files, but it is still too fast.

I've seen some mentions of buffered stream in the discussions, but not sure how I could add it here (and if that would solve the issue).

Thanks in advance for any and all help

Current code and mp3 files I use below:
Static_master.mp3
test2.mp3

#include <SPI.h>
#include <SD.h>
#include "AudioTools.h"
#include "AudioTools/AudioLibs/AudioBoardStream.h"
#include "AudioTools/AudioCodecs/CodecMP3Helix.h"

const int chipSelect=PIN_AUDIO_KIT_SD_CARD_CS;
AudioBoardStream i2s(AudioKitEs8388V1); // final output of decoded stream
OutputMixer<int16_t> mixer(i2s, 2);

//audio [1]
VolumeStream volume1(mixer);
EncodedAudioStream decoder1(&volume1, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier1; 
File audioFile1;

//audio [2]
VolumeStream volume2(mixer);
EncodedAudioStream decoder2(&volume2, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier2; 
File audioFile2;


void setup() {
   Serial.begin(115200);
   AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info); 
   

  //setup i2s / audiokit before SD!
  auto config = i2s.defaultConfig(TX_MODE);
  config.sd_active = true;
  i2s.begin(config);

  // setup SD
  SD.begin(chipSelect);

  //load files
  audioFile1 = SD.open("/demo.mp3");
  audioFile2 = SD.open("/Static_master.mp3");

  // set initial volume
  volume1.setVolume(0.8);
  volume1.begin();

  volume2.setVolume(0.5);
  volume2.begin();

  //setup decoders
  decoder1.begin();
  decoder2.begin();

  //start mixer
  mixer.begin(2048);

  //
  copier1.begin(decoder1,audioFile1);
  copier2.begin(decoder2,audioFile2);


}

void loop() {
    
    //copier loop
    copier2.copy();
    copier1.copy();

}