What sample rate should I choose?

I have a MacBook Pro with an external hd with my music on it. Some 24bit/192kHz, 24/96, 24/88.2, FLAC, 44 and 48. When I feed these files to my DAC, Wadia 321, should I be going into the Audio MIDI settings and choose the native resolution each time or should I set the MIDI to output 32/192 and just leave it?
Thank you.
Best is if you can purchase Bitperfect and then enable it to set Audio Midi to automatically set to whatever file resolution you happen to play... all on the fly.

Alternative set Audio Midi to 24 bit 96 KHZ and then launch iTunes - everything will be upsampled by iTunes to that resolution....
Listeners I respect say that 96 is the hearing cutoff
@djf1  I second shadorne's recommendation of BitPerfect.  Changes resolution for you, but also makes the sound better.  Clearer for sure.  Best $9.99 I have spent on audio, other than buying music. 

@fstein 192 is clearly better (albeit with diminishing returns) on my Yggy and approaches or exceeds vinyl.