Gbmcleod, I listen almost exclusively to acoustic instrument recordings, primarily jazz, classical, bluegrass, and some new age. Jazz big band at a reasonably high, but not deafening, volume is the acid test for me. It tests the balance of each part of the spectrum all at once. I am a former trombone player, and am very sensitive to the tonality of brass instruments. If it sounds harsh, edgy, or thin sounding at all I notice it. For me, instrument tonality is more important than the ultimate level of detail (but you have to have some of that, too).
Besides big band, solo trumpet, violin, and soprano sax can also sound unbelievably bad if there is any brightness in the chain. These instruments seem to produce a lot of harmonics which shows up harshness easily. Of course cymbals and triangles can give you an idea of the absolute level of the high frequencies and are valuable references also.
You're right, it is really tough to isolate the offending component when there are so many variables in the chain. In my experience of auditioning cables, I have found they make as much difference in the sound as any electronic component. When you think you have achieved a neutral and accurate sound, its hard to know if you did it by having all neutral components or if they simply complement each other well.
The only way I know of ascertaining which components are neutral is by trying out many types of each component in your system. Persistent colorations will stand out using this approach. For instance I know my speakers have a slightly soft treble. This is because after trying many combinations of components, this coloration has persisted. However, if the other components are very neutral, it is not a problem. It is only a problem if another soft component is in the chain, which exaggerates the coloration.
If you want to try some other ICs to see if your hardness problem persists I would suggest the following cables. None of these is perfect, but they are all basically neutral instead of acting as tone control cables.
Audience AU24 - the most neutral I've heard in the bass and mids. It has a soft treble, though, which was not compatible with my speakers.
Cardas Neutral Reference - Slightly warm in the mid-bass, but overall nicely balanced. One of these somewhere in the chain gives instruments their natural resonant sound, but two of them is a bit too much mid-bass. Far more neutral than Cardas Golden Reference.
Nordost Valhalla - Similar to Cardas NR except the lower bass and mid-bass is very slightly lean. Overall probably the best balanced cable I've tried but the others are so close, I don't think it's worth the money.
Nirvana S-X - Sounds almost identical to Cardas NR, but costs 3x as much.
Luminous Audio Sychestra Signature - slightly soft in the upper octave, but overall well balanced. The RCA version has less roll-off than the XLR version. The RCA version is a very dimensional cable. Soundstaging is among the best I've heard.
Good luck.
