Thanks for your work, Jokkipo.
To be fair, the audio situation in all forks of WiiSX I know is very messy and each one gives different results.
Using Vandal Hearts as an example of a game I know pretty well...
On the early pre-release version of WiiSX Lightrec by emu_kiddid that was shared some time ago, the sound is missing its echo-y/reverb effect, and it's missing instruments. But still, it wasn't supposed to be a public release and is work in progress, of course.
On WiiSXRX, the instruments seem to be there, but there is no reverb.
On Wiistation (I think it's 2.0 the one I have on my Wii) the reverb is there, but it's missing some instruments.
And on the version you've shared based on 2.4, it sounds like Wiistation but it has that delay (which might be from the original 2.4 version, I would need to test it).
With Wiistation versions, more than missing instruments, it's like they're there but get muted super fast with each note or their volume goes down to 0. Pretty strange.