Lack of bass with mac mini mp3/apple lossless file

Are you using 2 channels for music and a full set of surround speakers for movies?

Too much jitter from the Toslink on the Mac Mini. I would never use it this way for music. Your software choices are probably at fault too.

Consider instead an async USB converter wired with USB cable. S/PDIF coax to drive the DAC or SS decoder. These range from $100-$3500 depending on the level of sound quality you want. USB cables range from $50 to $800. 1.5m S/PDIF cables are $100-$1K. They should be 1.5m long at least. The top of the performance curve requires an expenditure of about $2600.00. This will beat even the best $15-30K CD Transports, so its worth it.

The other problem is likely your playback software and ripping software. iTunes on a PC or Mac does not cut-it. See these guidelines:

http://www.empiricalaudio.com/computer-audio/

Steve N.
Empirical Audio

Another option just occurred to me. You could continue using the Toslink output from the Mini, but feed it into a reclocker like the Synchro-Mesh and then to your DAC/Surround proc.. This will take care of the hardware jitter. A lot cheaper than a USB converter, and almost as good. Then you just need to take care of the software part of it.

Steve N.
Empirical Audio