FLAC, AIFF, WAV, and ALAC are all lossless formats, you should stick with these. Differences between them are entirely system dependent, if they exist at all. I have read that Amarra and Pure Music are both good software add-ons for Macs.
You have a DAC that can play hi res files, try some out at HD Tracks or Linn Records websites. I have not gone this route yet, and I don't use a Mac, so I am not sure about compatibility issues using iTunes/Amarra/Pure Music on a Mac to play hi res files. Depending on which Vlink you have, you might be limited to 24/96 on hi res.
You have a DAC that can play hi res files, try some out at HD Tracks or Linn Records websites. I have not gone this route yet, and I don't use a Mac, so I am not sure about compatibility issues using iTunes/Amarra/Pure Music on a Mac to play hi res files. Depending on which Vlink you have, you might be limited to 24/96 on hi res.