Well outfit and setup usually refers to the add-ons to a violin such as chin rests, shoulder rests, and fine tuners, mutes, electrical pick-ups and the like. It's like saying, how'd you dress your violin?

For example: My setup is a shoulder rest, a shallow chinrest and 4 fine tuners.
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I could be wrong though, and it might include maintenance items

The way I understand it, "outfit" includes the whole setup - fiddle, case, bow, shoulder rest, etc. Also describes an electric equipment system, pickup, etc.

"Setup" means how the fiddle itself is "dressed", if you will, describing the type of tailpiece, pegs, strings, bridge, etc. It also describes things like bridge configuration - a "fiddle" setup often has a flatter bridge and sometimes a lower nut, allowing quicker fingering and easier double stops. Luthiers say "fiddle" and "classical" setups when talking about repairs and adjustments.