New to this , so here goes-(and i looked for this question, couldn't find).
Have new MAc mini, just added PS Audio Digital III- now I cant play any of my HDTrack downloads- 9600?- Take it easy on the new guy- Using Itunes into Amarra Mini software--Any ideas?.also my $80 Rad-Shack works fine with this set up. Thank i advance-s
which input are you using...? Don't think the USB port can support hi rez.
HD Tracks uses flac files which i-tunes cannot handle. Not sure if Amarra works with flac - assume it does. I'm using PureMusic with itunes and I had to do a little fiddling with the settings in itunes to accept flac files. The amarra manual will tell you how. There is mac friendly software for flac files you can get for free, also.
How are the two being connected?
First thing to check for -- if you are connecting the Mac Mini to the PS Audio by USB cable, has the Mac Mini recognized the additional output and have you selected it as your audio output on the Mac? Open System Preferences, select "Sound", and click on the "Output" button to view the selected and available outputs. Your DAC should be one of the available outputs. If it is not already selected, do so, and see if that works. If you don't see the DAC listed as an output, check to make sure your connections are all solidly seated (it's easy to fail to fully insert a USB plug).
Meiwan raises a good point/possibility...Itunes cannot handle FLAC...I use Max to convert from FLAC to AppleLossless, and it's free and easy to use. Once you convert to Alossless, ITUNES will see and process it just like other music in your library....

AMARRA, while great stuff, is only a front end...and works with ITUNES

HOWEVER, you really need to tell us what you mean by "can't play"

Without knowing where you are's hard to for us to tell and help you.
K. Thanks to all- using USB cable to DAC. Thinking that is problem. High res transfer not happening. Amarra software says can not accept file , then shows 9600 not ok? Read somewhere need to use digital link instead of USB ? But why Rad shack working fine ? Also,PS DAC "upsamples"? So is it not set up to "just play" hi res?
Oh, and Amarra has built in Flac converter thingy to make new iTunes readable files. Hav done this. They will play thru iTunes only. Not thru Amarra. And play at 42(?) vs 96(?) that I prefer and had BEfoRe upgrade?!?
Upsampling and processing and outputting a high res signal are two entirely different things....I really don't think you're going to get high res from the USB port...however, as far as I know the optical will support it.

Good Luck.
Wrap up- seems the ps DAC isn't the right tool for my needs. Wanting to play native hi res files. Thus, unit is for upsampleing files. Plus I've learned standard USB does not support hi res file transfer. So... Back to drawing board and more homework. Gatta' love this hobby! Again-thanks to all who took time/effort to share....(at least I think I got what's goin' on)
Pick up a used hiface USB to spdif converter for around $100. I have compared the USB, optical and hiface with a ps audio dl3 and Mac mini and the hiface sounds significantly better to me. It will play sample rates up to 24/192 as well. USB is limited to 48 on the dl3 and the optical on the mini is limited to 24/96. You can also use some of the free players like audirvana to upsample your music to 24/192 which will be played natively into the ps audio dl3 when using the hiface. Prepare to increase your budget if you want to improve upon the ps audio dac.
I agree 100% with Johsti. That was my exact rig until recently and it solved the hi-rez issue and the sound was really wonderful. For $100 used the Hiface is a steal.