I have been making linear power supplies for the Mac Mini for a while and users are reporting it is avery nice upgrade sonically.
I asume you are talking about the 2009 Mini which has the isense resistor requirement. Here is a link showing you how to deal with isense :-http://www.computeraudiophile.com/files/Mac%20Mini%20PS%20Cable_0.pdf
I provide a very heavy duty version (6 to 10 amps) of the PR3 series 3 regulator called the PR3iEHD for diy Mac mini and Macbook Pro projects in voltage settings of 18v5 (Mini 2009), 16v5 (Macbook Pro), and 12v (Mini 2010 and 20011). You will need a big mains transformer (at least 160VA preferably 250VA) and a big heatsink of around 0.7 degrees C per watt. This is because linear supplies are not as efficient as switchers. However the benefits to sound quality are well worth the effort. I use the 12 volt vesion to power an a Pico powered Intel Atom dual core mobo in my audio server. The next step is to fit two more linear supplies for the 5v and 3v3 rails plus any housekeeping supplies and get rid of the Pico, when I get the time.
If there is any interest in this on DIY Paradise for diy builds Yeo might be prepared to stock these modules.