USB amp and speakers connected to Pi3/OSMC - low volume

I just connected my old Harman Kardon sub-and-speakers set (previously used on a Mac) to the Pi3 running OSMC. The system recognized the usb hardware, and selecting the correct item in audio output resulted in the sound coming out on the sub and speakers.

However, the volume is very low. With the master volume of OSMC at 100%, the sound is still very low. This sound system doesn’t have a manual volume control, so it plays at full effect by default.

When I connected a similar system, which is not USB, directly to the analog output the volume was great. But the analog output was so noisy as to be completely useless.

So, is there some mixer settings or similar that will help with this?

Just as FYI - there is experimental firmware from RPi Foundation that greatly improves the analogue sound. Feedback on the thread about it on RPi forum is that there are still some annoying issues (eg stopping after a while) but sound quality is good.

Try installing alsa-utils from apt and then check the output volumes with alsamixer.