Moving from PC to Mac

You can
a. use XLD (free software) to convert all your FLAC to AIFF or Apple Lossless
Both would retain the meta data of the FLAC files. XLD has a setting to "automatically add converted files to iTunes).

b. use something like Pure Music or Audirvana Plus to add FLAC files to iTunes.
This method does not do any conversion. PM/A+ creates a "shortcut" to your FLAC files (in ALAC format) that you can view in iTunes. When you select the file for playback, PM/A+ works in the background to dynamically play the FLAC file using its own playback engine (which is superior to iTunes')

Method b means that the generated files don't work when you sync it with an iPod or iPhone etc though. But if this is for a music server, it should be fine.

I recommend Audirvana Plus as it also plays DSD files, sounds great and is cheaper than most of the other options (last time I checked). I have PM and Amarra as well (having bought Amarra when it was over 500 bucks! so I think I am unbiased here).

I got downloaded flac files, I am on mac. I simply downloaded an app from itunes store, it costs 9.99 and it converts any format to any other.It does it super fast. All you do is drag the files to be converted into the music converter opened Window choose destination drive, in my case it's an external usb drive, and click convert.Simple,fast,reliable.I personally found XLD clunky.
Regards
George

I use XLD also because it has an EAC-type ripper for CD ripping.

Why convert the files? Use Cog for playing back your flac files on a Mac.