Most of the early games made by the id Software guys only support PC speaker sound.

I suggest checking the "Specs" tab at MobyGames as a guide for what games do or do not support, but keep in mind that it is not definitive: https://www.mobygames.com/game/dos/rescue-rover

You are right about Rover 1 (didn't actually looked at that one).

But for Rover 2, the readme states:

"If you have an AdLib, Sound Blaster, or Sound Source, you can choose to have the sound effects play on them."

Also the in-game menu has an option to use AdLib or Sound Blaster (both greyed out, though, so not detected by the game, it seems). I tried reducing cycles before launching the game, because for other games cycles being too high seemed to be an issue to detect the sound blaster, but here it doesn't help.

The sound effects seem to use adlib, but sound blaster is greyed out... Music is totally greyed out.

It appears to be a false claim of support for SB and DSS, or perhaps just a misunderstanding because the interface is misleading.

The game has only simple speaker and OPL sfx, no PCM, no music. Why did they leave the music on/off tab in the interface when there's no music? I suppose because it was easier to force the "off" setting than remove the option completely from the interface, and so it may be with the sound options.

If you read the history about id Software and Softdisk toward the end of their relationship then you'll perhaps gain an understanding of why some corner-cutting occured.

So the info here is also not correct, then?

https://www.mobygames.com/game/dos/rescue-rover-2/techinfo

Apparently so. As I mentioned, MobyGames is not definitive -- it doesn't dissect a game to verify what is printed on the game box or what the publisher claims. Blame the misleading interface for the confusion.

Perfect. Thanks for the clarification!