Creating an audio-only stream from a live stream

I am using Flash Media Live Encoder (3.2) to send multiple bitrate streams to an instance of Adobe Media Server 5. In addition to the video streams, I am trying to generate an audio-only stream.

I am using the default 'livepkgr' application. The input stream contains H.264 video + AAC audio.

The stream name that I set in FMLE is set to this:

livestream%i?adbe-live-event=liveevent&adbe-audio-stream-name=livestream1_audio_only&adbe-audio-stream-src=livestream1

I created a variant playlist to include the audio-only stream. It looks like this:

#EXTM3U 
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=150000 
/hls-live/livepkgr/_definst_/liveevent/livestream1.m3u8 
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=500000 
/hls-live/livepkgr/_definst_/liveevent/livestream2.m3u8 
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=700000 
/hls-live/livepkgr/_definst_/liveevent/livestream3.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=64000,CODECS="mp4a.40.2"
/hls-live/livepkgr/_definst_/liveevent/livestream1_audio_only.m3u8

However, when I retrieve the audio-only playlist it contains a list of .ts files. If it was working correctly I would expect there to be a list of .aac files. Here's an extract from the playlist (livestream1_audio_only.m3u8😞

#EXTM3U
#EXT-X-MEDIA-SEQUENCE:1927
#EXT-X-ALLOW-CACHE:NO
#EXT-X-VERSION:2
#EXT-X-TARGETDURATION:8
#EXTINF:8,
../../../../hls-live/streams/livepkgr/events/_definst_/liveevent/livestream1_audio_onlyNum1927.ts
#EXTINF:8,
../../../../hls-live/streams/livepkgr/events/_definst_/liveevent/livestream1_audio_onlyNum1928.ts
#EXTINF:8,
../../../../hls-live/streams/livepkgr/events/_definst_/liveevent/livestream1_audio_onlyNum1929.ts
#EXTINF:8,
../../../../hls-live/streams/livepkgr/events/_definst_/liveevent/livestream1_audio_onlyNum1930.ts

Any ideas why it doesn't seem to be working?

Thanks