New setup with computer as source??

Ultimately, it will come down to your personal preferences, but a Wavelength Brick USB DAC coupled to a Mac Mini should be a good choice. Since you are using a Shanling tube CD player, a tube DAC like the Brick should be a nice improvement. Just remember that you should use another outboard hard disk drive (7200 RPM rotation speed) to store all your music files, either in Apple Lossless or uncompressed 16-bit, 44.1kHz PCM (AIFF) file format. The hard drive should be connected via FireWire 400 like one of the LaCie mini hard disk drives that stack underneath the Mac Mini. Since FireWire (a.k.a. IEEE 1394) is common with the Mac hardware platform, stay with a FireWire drive and do not use a USB 1.1 or USB 2.0 drive. In most circumstances, FireWire busses operate at higher transfer speeds than USB busses. Also, connect your USB DAC directly to the USB 2.0 port on the Mac Mini. You'll probably want a decent USB 2.0 cable like a Monster Cable brand cable to connect the DAC to your Mac Mini. Do not use a USB expansion hub as this could compromise the quality of the USB digital data transfer, especially if you have multiple devices connected to a single USB port. Refer to Wavelength Audio's Web site and instructions for proper setup of iTunes and the Brick DAC, and you should have a very nice PC transport and DAC digital front end.

Also, keep your media drive defragmented as you rip your CD collection. Mac OS X does this automatically, but if you want to do it manually, there are disk defragmenting utility programs like Coriolis' iDefrag that can help you maintain your disk drives for optimal performance.

that's more or less exactly what I was planning on. however, the brick seems a bit much to put between an inexpensive computer and the amp. what about a headroom product like the total bithead (headphone amp) instead? it would at least improve on the built-in mac mini soundcard, right? - and what about (for the sake of the argument) going into a receiver that has USB (like the outlaw rr2150) - would this not make the brick unnecessary and allow you to use the built-in DAC?

The reason I want to use the Brick is because this new setup will REPLACE my CD player as a source, not simply be a supplement or secondary setup. I thus want the best possible reproduction of music.