Hi pierini1,
You need the following Bios ROM ym2608.zip :
<game isbios="yes" name="ym2608">
<description>YM2608 Internal ROM [Internal ROM only]</description>
<year>1989</year>
<manufacturer>Yamaha</manufacturer>
<rom name="ym2608_adpcm_rom.bin" size="8192" crc="23c9e0d8"/>
</game>
This bios is requested for wc90, sformula, tail2nos, etc... as they use board-ROMs from YM2608.
Bootleg wc90 clones don't use board-ROMs from ym2608.
Best regards,
JacKc.