Question about Logitech Z407

Unfortunately that's not possible. I don't turn it off any more. I looked at the standby power consumption and it's almost zero.

This start sound at full volume is absolutely annoying. You should not buy this product.

It also bothered me enormously, especially when my wife wanted to go to sleep... I managed it, but I don't know how :-( Maybe it's because I connected the Z407 to the PC via a 3.5 mm jack instead of via Bluetooth, and set it that way via the PC settings? In any case, it remains mute now.

It is not possible to turn off the startup sound.

I can't answer that. I don't use it myself. It was bought as a gift.