Thank you both. Are you referring to a battery powered box? I found the "Saramonic Smartrig" 2-channel box for example that has two XLR inputs and a 3.5mm output.
Or are you referring to boxes powered by the camera itself, or in some other way?
No, the camera can't power anything unless the something attaches to the hot shoe on its top.. like most shotgun mikes do. But these are more oriented to interviews, sound capturing, filmaking etc - as opposite to studio recording.
With a (non battery-powered) condenser studio mic, you will have something like:
Mic -> XLR cable -> phantom power box input -> phantom power box output -> XLR/Jack cable -> 2.5mm adapter -> camera mic input
As of powering the box itself, there are various types. The electricity can come from a battery, or AC power, or both - for example the ART Phantom PRO is only battery powered, the ART Phantom PRO mk II can be operated both ways, while the cheap Subzero single-mic supply uses AC only (if I understand well).
Do not discount microphones with a built-in battery (I already mentioned the Røde NT3 or mic compatible with the Sennheiser K6 system for example.. but you could get a uber-expensive vintage U87 with battery power! :D). It's not so common so it's hard to find specs (when I bought my NT3 I didn't even know it had battery) but may worth a little search, as the less clutter you have when recording video, the easiest it is. If it's for once in a while, tough, a phantom power box works fine.
Keep in mind you could also try with a good dynamic or a ribbon - no power required in that case. A ribbon especially would probably suit a violin very well, and there are more than decent offering at a good price, for example SE Electronics had one I think. I've used myself a Shinybox in many occasions with fantastic results.
Another problem is where do I attach the box, to the mic stand? To the tripod?
Sorry for the naive questions.
Nothing to be sorry about!
It really depends on how you shoot video - if you hand hold the camera, if you use a tripod or a shoulder mount..
In general if you use a phantom supply, you will have a XLR to jack cable (terminated into the 2.5mm adaptor) coming out of the box, so with a long-ish cable you can just leave the box on the ground. The cable can be a little heavy tough (especially since the MFT cameras are so light!), so if you hold the camera directly in your hand, it will get a little getting used to (but you can simply strap the cable on your shoulder so that only a small amount of weight is on the camera).
When I'm using a tripod, and I intend to move the tripod for different sequences, just use velcro to strap stuff directly on the tripod itself.
For example I use bulky Sony NP F-970 external batteries to keep shooting all day using a "fake battery" cable to power the camera., and attaching it to the tripod via velcro straps makes sure it doesn't suddenly disconnect mid-take. :D
A cheap chinese grip (I've used one like this quite a bit at the beginning) will give you someplace else where you can velcro stuff - and if you plan not to use a tripod - it's almost a must with the G6, which doesn't have any form of body stabilization.
But really your fantasy's the limit - you can generally go full monthy as here for example :D
Note - all the links I've placed here are just for illustration, I didn't make any effort to find the cheapest/better products, but it's just to give you an idea of the options.. ART stuff is generally good tough.