Dmitrydr, yes both NR and AU24 can be perceived to lose some details if your system is already on the warm side. If your system is a little bright, however, they might be exactly what you need. It is pretty hard to "soften the highs" as you requested, without cutting the details somewhat. I would say NR preserves the details a little better than AU24. All I can say is try it. I've found you have to try many cables before you can be certain you have the best one for your system.
If you do try Cardas NR, be sure to give it at least two weeks for break-in. It sounds very compressed at first, but opens up over time.
Luminous Audio Synchestra Signature is a copper cable that is extremely neutral and has great soundstaging and low-level details. It won't warm up your sound, though.
Another possibility that might work for you is Kimber KS1030/1130, but it is quite expensive. This is the best IC I've heard. Very tonally neutral, but still lets you hear very low-level things clearly.
If you do try Cardas NR, be sure to give it at least two weeks for break-in. It sounds very compressed at first, but opens up over time.
Luminous Audio Synchestra Signature is a copper cable that is extremely neutral and has great soundstaging and low-level details. It won't warm up your sound, though.
Another possibility that might work for you is Kimber KS1030/1130, but it is quite expensive. This is the best IC I've heard. Very tonally neutral, but still lets you hear very low-level things clearly.