https://www.synology.com/support/developer#tool, find "Audio Station Guide"
Requires Audio Station version 5.0 or above.
Audio Station 5.0 is currently in beta stage (released with DSM 4.2 beta). The built-in lyrics module can search lyric from LyricWiki (http://lyrics.wikia.com/). But due to copyright issue, LyricWiki API only provides partial lyric, not full lyric.
There are already user-made lyrics module available to search lyric from other sites.
Provided by ajoman
o ChartLyrics (http://sdrv.ms/V5KMqe)
o LoloLyrics (http://sdrv.ms/11BvNJV)
Found in Chinese forum
o SynoAUM-TTPlayer (http://sourceforge.net/projects/synoaumttplayer/)
Found in a Chinese blog
Another plugin for Chinese
Updated 2019 0824:
o Genius [fujirou_genius post]
o MusixMatch [fujirou_musix_match post]
o KKBOX (Chinese) [fujirou_kkbox post]
o MetroLyrics [fujirou_metro_lyrics post]
o LyricWiki (with complete lyric) [fujirou_lyric_wiki post]