Unfortunately, I haven't had any luck ripping the instruments from Darius - The Sea Track. The chip is a YM2203 (OPN).
VGM2PRE only works with YM2612 (OPN2) and YM2151 (OPM).
GENNY is 2612 and VOPM is 2151. Because the chips have similar parameters, some instruments work in both programs. However I haven't found a program to rip instruments from the arcade chip - YM2203. Sorry, man.
It's possible to copy values from MDPLAYER to GENNY, however it's difficult because GENNY doesn't have numbers for all the parameters.
VOPM is easier because it's possible to copy exact numerical values from MDPLAYER to VOPM.
I remember the VOPM VST wasn't working previously, maybe give it another try... There are both 32 and 64 Bit versions of VOPM.
http://www.vst4free.com/free_vst.php?pl mp;id=1066
Furthermore, to convert a VGZ to VGM, just rename the file type from "vgz" to "vgm.gz" and extract the file like normal. I use WINRAR. VGM players like MDPLAYER and VGMPLAY will play many different kinds of chips, so it's easy to listen any VGM, however extracting the instruments is more challenging because it depends on whether a program is compatible with the specific chip used in the VGM. Sorry I couldn't be of more help. Good luck!