So the Matrix HD60 speaker cables are in (much better spades, BTW)... Clearly, with the HD60/50 combo, the tonal balance is restored quite a bit to make it very enjoyable again, but still the new combo is not as powerful in the bottom end as the old. And when one cable restores the tonal balance of the other, that to me is a tone control. Cables should not add or subtract. On the other hand, the HD60/50 pair does appear to lift a very thin veil with just a tiny bit less smearing, which you can hear if you swap in and out quickly. It is evident with some instruments more than others, like cellos. I have played the same Sinfonia da Requiem dozens of times, back and forth, and it is true there is just a tiny bit less smearing which makes instruments more lifelike, and more importantly the soundstage a little more well defined and a tad deeper - that's because there is tighter focus on each instrument; I also noticed the cymbals are a bit sweeter. But you really have to listen intently to pick up these changes.
As a combo, the new cables work very well _together_ - so I would not upgrade one without the other. Overall, it is important that the quality of the old cables is largely maintained, with tiny improvements. I can see why 1rsw would want to seek more of it, by going up the ladder. Frankly, I hate to say this, but I would start at the next level, the HD90; and I still don't like the interconnects as I appear to like the speaker cables - I really hope there will be another set of ICs. I am continuing the audition through the weekend, but the price is too steep for such a small gain - a gain that's not universal either to these ears.