Unsure if it'll be the same trouble I had on my Dell Optiplex 755 with 9.10, but it worked for me.

I had to open the redesigned Sound Preferences, go to the Hardware tab, and select the right 'Profile' for my hardware device. In my case I've got a Plantronics headset (shows up as USB DSPv4 Audio Interface) and it was set to be "Digital Stereo Duplex". With that setting, the audio would be very quiet at maximum. Changing this around to "Analog Stereo Duplex" makes the max volume very, very loud now. So much so that I can only use the headset on 25% before it gets painful.

I suppose it'll depend on many things, but switching that profile solved the problem.

Cheers