On the Debian Wiki (wiki.debian.org/RaspberryPi), there’s these comments about overclocking the RPi; would they clash with any aspect of Volumio?
Overclocking is quite easy and convenient, and doesn’t invalidate your warranty if you don’t change voltage. It happens that the actual L2 speed of the Raspberry Pi 2 is severelly underclocked, making the device much more slower that it should actually be. There has been reports of users using overclocked speeds of the processor and the L2 for months without a single issue, but you must be carefull in respecting a good proportion between L2 speed and processor, and overclocking the RAM is generally not recommended.
Try this setting, it has demonstrated to be stable and doubles the speed of this small machine in general. Edit /boot/config.txt and substitute or add these lines: