Best Digital Input from PC to DAC

Agreed, if money isn't a concern get Steve to hook you up with one of his options and skip all the experimenting. If value is a concern there are lots of cheaper alternatives to keep you busy.

What DAC are you using? Many USB enabled DACs aren't doing it right and will give you less than the best results.

If you want to stick to the simple computer/DAC solution, I have liked what I've heard from DACs with an asynchronous capability. This allows the clock in the DAC to control the data stream from the computer. Wavelength USB DAC is a good example of this approach.

If cost is no objective, then Emperical Audio components seem to me to be the best technical execution of computer/DAC my opinion. It often means adding and/or modifying components, but I2S blows away most other connections in terms of minimizing errors.

An alternate path (which I prefer) are the "single device" solutions like the Slim Devices Transport that send a raw data file to the device where it is decoded, converted to digital stream and run through D/A conversion on one circuit board. This represents the fewest potential places for problems in the signal path. If you look at the ModWright Transporter, you are pretty much matching the best source components out there for under $4,000

More choices are on the way in the coming months, but you are on good footing right now and aren't missing anything earth shattering.

For the record, I run FLAC files through WinAmp with the ASIO plug-in myself (I like the WinAmp better than Foobar - just a personal preference). I also run a modified Sonos network to my DAC for non-critical listening. Lastly, I have a Fubar 3 headphone amp/USB DAC with Sennheiser headphones at work - great sound for under $300.

Hope you are having as much fun as I am!

My setup involves a Vista desktop or XP laptop to firewire Focusrite Saffire LE, Paradisea+ NOS DAC with Bendix tube output stage, the non-USB version, a NuForce processor, Gemstone amp, and Selah Audio 5.1 speaker setup. Using FLAC and either Foobar or Media Monkey. Speaker cables are twelve guage wire and homemade, silver series interconnects, stock firewire cable. Various configurations are possible. I've never really got around to a proper home setup since the basement is still not finished.

Look into firewire. Much better than USB.