As OG says. There are a few options;
For sound get one with a jack plug and get some helmet ear pads which are speakers in a pad shape that fit in your helmet or, get a bluetooth one and a bluetooth helmet speaker system.
For power either use the satnav internal battery or, use a direct power feed into the battery or, look at a company called "so easy". They produce a battery pack (and bag) that is recharged from a USB socket abd can boost the time you can use a satnav.
For holders look at things like the "held tiny bumbag" which is a satnav sized magnetic tank bag or, just the map pocket of your current tankbag or, something like the "ram mount" sysyem or, the "so easy" bag option.
OG has the enclosed case option. At the moment I have this type of setup HERE Tucked under the fairing.