How important is a preamp for purely digital sources?

There is another aspect to this entire discussion that has not been touched upon. While a preamp may be technically perfect and not enhance or degrade the sound there are two more links added to the chain with an external preamp that need to be considered. The interconnects. I have yet to find an IC at any price point that does not "color" the sound or add noise. I'm a firm believer in the concept of less (quantity not quality)  is more when it comes to ICs. 

jrapp, a well engineered integrated can solve that problem 

I know that but integrateds were not the subject of this discussion. preamp (s) are. When considering how important a preamp is (subject of discussion) and its effects on digital sources one must not forget the IC part of the equation. Years ago I added a very pricey and highly regarded BAT VK51SE to my then all digital system. I had used a pair of highly rated mid/high-line Audioquest ICs that I had from a prior system. The results were not as expected. The sound lacked warmth and was slightly muddy; that is until I replaced the ICs with Synergistic Resolution Reference Active series IC’s. The difference was astonishing; the expected tube warmth was now there and the muddiness was gone. This experience leads me to wonder if the results that some posters are touting are really the result of the preamp addition of the effects of the additional ICs.

Cables, are mostly snake oil, and differences are the most minute of any part of the audio chain, and are particularly small compared to those of the speakers. Don't understand why companies aren't being charged with fraud for making false claims about boutique cables. What's George Cardas new product now, the, "Cardas Clear Power Cable is George Cardas’ midrange Clear-series AC power cable.", which, "is designed for applications where you need a bit more current capacity and a higher degree of filtration than Clear M Power Cable, but you don't need a large, high-current power cable like Cardas Clear Beyond." Interconnect differences are inaudible for 95% of the general population if the connectors are clean and the wiring doesn’t add capacitance, or inductance. On the other hand, somebody would easily be able to tell that my power amp is on the warm side. If the system has EMI that happens to be picked up by the interconnects, then it's best to deal with that at the source. I have DH Labs Silver Sonic BL-1 Series II interconnects that I made myself specifically so I could make them as short as possible, and have heard zero difference compared to OEM cables, particularly with the short lengths that I use. It’s still available for $7 a ft on Ebay, and the ad says, "SILVER SONIC BL-1 Series II Interconnect is a high performance audio interconnect cable that combines the highest sound quality and reliability available at its price point. " Sure. Whatever that means. It's designed as balanced, and comes with a shield, but I don't use XLR in my system; my amp and sub can't do it. XLR had been designed for professional applications, to reject interference for the longer cables runs used in the field, and this could add little value to most amateurs.  People can reduce noise, by keeping cable runs short and away from noisy things like motors and VFD's. I have also used some BL-1 inside my power amp and that's the only place I’ve grounded the shield (it's a noisy power supply). You can use twisted pair cables to try and reject interference, but again, there's little of that in my system away from the power supplies. People can use ferrite beads or rings from Digikey to reject EMI in a a DAC or amp, or better yet, peel and stick foil. I have used it to try and keep power supply noise away from other parts of the circuitry. I can't detect how bad it is without an oscilloscope.

dookie30:

Take a look at a McIntosh D150 or perhaps a D100. My be a little bit more than you are want to spend but consider the axiom of buy it once and save in the long run.

I owned a D150 till I upgrade to a D1100 which I run now. The D150 will mate will with your Mac amp. Use the resonable S/PDIF out to the D150  from you Node and a decent set of analog lines to the amp. The D150 will perform volume in the analog domain. 

One thing that is rarely discussed with DACs is the analog output section. This is very import to the overall sound and vibe of the DAC (in this case digital preamp) and what works for one might not be a good choice for another. That said, since you have a McIntosh amp you might like the overall synergy from the two pieces. Also, if you want you can hook up other digital sources as well as a McIntosh CD/SACD transport where the DSD will be connected via a custom DIN connector. 

Very happy with my setup and the D150 seems to be going for around $1.5k to 1.8k these days. Find a nice one and be happy.