Asterisk mp3 mono monitor vs stereo monitor (left channel - one side, right channel - another)

[macro-recording]
exten => s,1,GoToIf($["${RECORDING}" = "1"]?yes:no)
exten => s,n(yes),Set(fname=${UNIQUEID}-${STRFTIME(${EPOCH},,%Y-%m-%d-%H_%M)}-${ARG1}-${ARG2});
exten => s,n,Set(FULL_DIR=${DIR_RECORDS}${STRFTIME(${EPOCH},,%Y)}/${STRFTIME(${EPOCH},,%m)}/${STRFTIME(${EPOCH},,%d)}/)
exten => s,n,Set(monopt=nice -n 19 /usr/bin/lame -b 32  --silent "${FULL_DIR}${fname}.wav"  "${FULL_DIR}${fname}.mp3" && rm -f "${FULL_DIR}${fname}.wav" && chmod o+r "${FULL_DIR}${fname}.mp3");
exten => s,n,Set(CDR(filename)=${fname}.mp3);
exten => s,n,Set(CDR(realdst)=${ARG2});
exten => s,n,MixMonitor(${FULL_DIR}${fname}.wav,b,${monopt});
exten => s,n(no),Verbose(Exit record);

[macro-stereorecording]
exten => s,1,GoToIf($["${RECORDING}" = "1"]?yes:no)
exten => s,n(yes),Set(fname=${UNIQUEID}-${STRFTIME(${EPOCH},,%Y-%m-%d-%H_%M)}-${ARG1}-${ARG2});
exten => s,n,Set(FULL_DIR=${DIR_RECORDS}${STRFTIME(${EPOCH},,%Y)}/${STRFTIME(${EPOCH},,%m)}/${STRFTIME(${EPOCH},,%d)}/)
exten => s,n,Set(monwav=nice -n 19 /usr/bin/sox -M "${FULL_DIR}${fname}-in.wav" "${FULL_DIR}${fname}-out.wav" "${FULL_DIR}${fname}-joint.wav" && );
exten => s,n,Set(monmp3=nice -n 19 /usr/bin/lame -b 32 --silent "${FULL_DIR}${fname}-joint.wav" "${FULL_DIR}${fname}.mp3" && );
exten => s,n,Set(moncleanup=rm -f ${FULL_DIR}${fname}*.wav && chmod o+r "${FULL_DIR}${fname}.mp3");
exten => s,n,Set(CDR(filename)=${fname}.mp3);
exten => s,n,Set(CDR(realdst)=${ARG2});
exten => s,n,MixMonitor(${FULL_DIR}${fname}.wav,bSr(${FULL_DIR}${fname}-in.wav)t(${FULL_DIR}${fname}-out.wav),${monwav}${monmp3}${moncleanup});
exten => s,n(no),Verbose(Exit stereo record);