wrote:

I tried Virtualbox which doesn't simulate the old OPL3 MIDI device,

As I read from he

https://forums.virtualbox.org/viewtopic.php?t=9918

============
2. Sound /Audio Integration.

In VirtualBox, you must enable Sound, and use "Sound Blaster 16".
It is available since VBox 1.6.0.

The procedure for installation is rather simple:
NOTE: The procedure below is only needed if you switch from AC'97 to
SB16.
It is not needed, if you create new VM with SB16, then install Win98 on
it.

2.1. Delete your sound card device and all unknown devices from "Device
Manager".
2.2 Add New Hardware (from Control Panel).
==============

Now I don't know if Virtualbox will emulate AC97 sound when running
Win-98, but even if it can't (did you try?) I would have thought that
"Sound Blaster 16" device would have had midi functionality.