what digital cables for my dac?

Tobias, yes, I've tried 1.5 meters in digital cables. I think it has much to do with what cable you're using. I read a statement by Ray Kimber that their digital cables tend to have more upper-frequency emphasis in shorter lengths, which is my experience listening to a number of different cables. I found the shorter length cable to present a more realistic sound on percussion.
I think people should just trust their own ears, if 1.5 meters sounds better to some, and .5 better to others, who am I to say they're wrong? I suspect that the improved rise time in shorter lengths may offset any possible increases in reflectivity. But that's just speculation on my part.

i've been very satisfied with the original ps audio top of the line digital cable. i believe it was $300 list when it came out.

the original illuminati cable is another good choice.

Mrtennis, I agree, the xstream digital from ps audio was an overlooked gem. I suspect alot of people didn't care for it because of it's extremely revealing character.
The digi-cable from Discovery cable is another standout, but too inexpensive to be taken seriously by some :)

I know the use of a longer length seems counterintuitive to those of us who are used to "shorter is better". Shorter _is_ better, for analog cables.

Go to http://www.empiricalaudio.com. Scroll down to the link "Paper on S/PDIF cable length in PSOnline".

In a nutshell, this paper explains that signals are reflected internally in digital interconnects. Good DAC design can minimize these reflections but this is usually not done. In shorter cables, the reflected signal returns to the output very close to the rising edge of a wave, and confuses the DAC about the timing of the signal. The result is jitter. The longer length allows the reflection to return at a time when it is less likely to be confused with signal. The result is more coherent music.

(I apologize for any inaccuracies which may be found in the very brief summary above.)

You can also refer to Chris Ven Haus' Web site, where he specifies that 1.5 meters is optimum length for digital interconnects, and to UHF Magazine number 74. UHF tested different cable lengths and now do not recommend any length shorter than 1.5 meter.

UHF Magazine

I did my own tests and came to the same conclusion. I used 1-meter and 1.5-meter lengths of 75-ohm Apogee Wyde Eye (still a contender for best at its price point). We listened using my TEAC VRDS T1 and Apogee DA-1000E-20, and also a friend's Theta Universal and Kora Hermes. The results were unquestionably in favour of the longer length.

You could try a test yourself and see.

First of all, let me say that I'm not trying to prove anyone here wrong for believing that 1.5 meters is the 'best' length for digital cables, but I am trying to show that there certainly is not a consensus on the subject. According to Dan Lavry of Lavry Engineering, that Empirical Audio SPDIF article is "nonsense": http://recforums.prosoundweb.com/index.php/mv/msg/11678/0//0/

Tplavas, I appreciate the reference to Mr. Lavry's article and I shall certainly follow it up. Thank you.

I would just like to point out that "believing" is not the appropriate word in my case. If I understand the word "belief" correctly, it can be used to refer to something that one has not witnessed with his own senses, but has heard reported.

I do not base my statement that a longer cable may be better on articles that I have read. I made up two cables identical in all but length and listened to them with a friend, on our two systems. That makes just four trials, or two comparisons, in my experience.

With our gear, in our rooms, and with those cables, the difference was very clear, so I can say from experience, not from belief, that in these trials longer was preferable. I recommend that anyone who has not heard such a difference base his or her final conclusion on experience too. I only mention my own to encourage others to try it--not to encourage others to spread the word on something they haven't heard. It has the advantage of being a relatively inexpensive improvement; that is, if it works for you.

I have also heard at least one much better system than my own which nonetheless uses a 1-meter digital interconnect. Perhaps the owner would be happier if he tried a longer cable, I don't know. He is certainly happy now.