Hello! I just tested it on the latest version of Furnace (0.8.6.3), and the volume works fine on my end. It might be related to your system or setup, maybe? To troubleshoot further, I'd recommend trying some sample songs from other artists that also use sample instruments, to see if those are quiet as well. If they are, it's likely a general issue. It may be worth it to reach out to the devs. Hope this helps!