Pros - Improved soundstage, sub-bass, mids, clarity, detail and accuracy.
Cons - The internal wire is expensive
(science guys feel free to ignore this review. Thanks)
As most people know by now, I've always disliked most Sennheiser headphones. They're not bad, but the sound from the HD-600 and HD-650 just doesn't engage me and is not that fun. They're not clear enough, don't have enough detail or treble or are muffled. I previously had the HD-650 and HD-600 twice with various amps. The HD-600 is good, but it's not for me. Loved it for movies and games though, but for music it put me to sleep.
When I got the HD-598 I loved it. Compared it to the HD-600 and HD-650 and just preferred the signature of the HD-598 despite the others being "technically better".
I recently got this cable in and was shocked at the differences between it and the stock cable. I've always felt that most recables made less than a 5% difference in sound. I do my own DIY recables. Recabling the HD-598 made the biggest difference. I use a cheap wire that costs 60 cents per foot and it sounds better than stock but has the same signature mostly. Even adding a new cable to a Q701 made under a 5% difference. I actually now prefer stock cable. I think it's due to the internal wires still being intact.
With this cable the mids are much more engaging and not so anemic. They sound more forward, but I don't know for sure this is the case. Luckily the cable retains the warmth of the HD-600 and doesn't make it less warm. If you use other wire, you can make it even warmer, which is a negative for me. Canare or Mogami does this.
Next, i'm noticing much better sub-bass. The low bass rumble in video games is now much more present. I don't know how a wire can add bass and that'd be impossible right? But this is my impression. I've noticed ZERO change in mid-bass quantity.
The biggest difference is in sound clarity, accuracy and detail. The HD-600 is now crystal clear. Yes, it was a shock for me. What the heck? There's some detail in there that I can usually only hear on my Q701 and KRKs. Yeah..from an HD-600! So, is the HD-600 now a detail monster? Huh?!
With stock cable I've noticed that any badly recording or harsh recordings are not too bad for the ears. They don't sound bad like they should. Some may find this a plus, but I don't want my headphone doing anything to "fix" my music. With this cable, bad songs are very bad and not "tamed" to sound any better. I don't notice any boost in the treble, but it's possible. If anything, it's slightly in the mids and sub-bass. I'd like to think it's just fixing the deficiencies of the stock cable.
Now the science guys will also love this, but the soundstage is very much improved. With gaming and specific music it's almost like an out of head experience. Not like the Q701, but pretty impressive.
The HD-600 with this cable is comparable in sound quality to the Q701 almost. Q701 will have a larger soundstage, more treble and is slightly less forgiving. A little bit more clear too and less warm.
This review was based on about 4 days of listening. Here's the fact: I don't enjoy the HD-600 at all with the stock cable. It just doesn't do it for me. Love it with this cable. Good enough for me. Don't ask me how this is possible.
With stock cable on the HD-600 I prefer the HD-598. With this cable I may end up preferring the HD-600 over the HD-598. I need to give it a few more days.
I can't put the improvements into a percentage, but it was enough to make me love what the HD-600 is capable of. I'm now a believer that the stock Sennheiser cables are no good at all and really holds the sound back. It was the case with the HD-598 (that I recabled) and now the HD-600. Copper is copper right?
Another thing that I found interesting. When using NO dac and a portable player the differences between stock and this cable are harder to spot. When I use my HRT Music Streamer II and Headroom Micro Amp, the differences are stupid easy to spot. I wonder why this is?
For anyone that is thinking of getting the HD-600, here is what I suggest instead of buying the $400 new pair. Find and HD-600 used and have someone make this or find a used one. You can even make one yourself if you want. You would end up saving probably a hundred dollars even if you had one made. If you don't believe in cables, even try one with say Belden 1192A or something similar. I remember I once believed cables all sounded the same, but now I don't after making my own (cheap) cables. I think a good amp and DAC play a roll in it too. I actually couldn't tell the difference between K702 cables before I had a good DAC. Don't know why. With some headphones the benefits are small. I guess it depends on the quality of wire.
I've tried HD-600 recables with Mogami and Canare and this is much better. Worth the extra money and it's still not too expensive. I'd pay up to $200 for the improvements I've heard (crazy, I know), but not over that. On the Q701 I've not heard a cable that made $100+ worth of difference..yet. I think the benefits of that are chopped in half due to the internal wires though.
Tempted to give the HD-650 another try now thanks to this wire...must resist.