2xYM3812: Music sounds wrong in Battlantis

[Fungi66]

(Bug report from mametesters.org) (https://mametesters.org/view.php?id=8391)

The Main BGM on the 1st act in Battlantis from Konami sounds wrong after the OPL rewrite for MAME 0.231. Battlantis sound hardware is quite unique in that it uses 2 YM3812 chips for both the sound and music.

PCB footage of the game: https://www.nicovideo.jp/watch/sm29650400

Here's what it sounds like currently in MAME: https://mametesters.org/file_download.php?file_id=6160&type=bug
Here's what is sounded like prior to the rewirte: https://mametesters.org/file_download.php?file_id=6161&type=bug

And if it helps too, here's a link to the vgmrip of Battlantis: https://vgmrips.net/packs/pack/battlantis-arcade
Thank you for your amazing work Aaron;)