IMHO, these are absolutely the best sounding IEMs I have used to date. This includes: (The Empire Ears Raven, Astell&Kern x Empire Ears NOVUS, Aroma Audio Fei Wan, UM Multiverse Mentor, Noble Audio Viking Ragnar, and Noble Audio Ronin). They easily punch above their price point in terms of sound quality characteristics and capabilities.
The Timbre/tonality is at the very least on par with the Aroma Audio Fei Wan. The dual BA custom "Diablo" bass drivers sound like TOTL quality Dynamic Drivers. Unless someone told me I could have sworn these were using top notch Dynamic Drivers. The sub-bass is the best I've heard. Nothing has beaten the Unique Melody Multiverse Mentor in terms of creating a holographic soundstage that feels like it surrounds you a full 360 degrees, but Macbeth's imaging and holography are TOTL god tier level, The treble detail is also TOTL without any sibilance whatsoever. The customized dual Sonion BCDs that only work in the Mids to High-Mids region creates a truly unique effect for vocals.
I don't want to get into a debate whether different conductivity metals in different audio cables can change or improve the sound over the stock cable. I'm simply here to relay my own personal auditory experience. Having said that:
The Stock Eletech copper cable is very good, it provides plenty of detail and gives a slightly warm tonality to Macbeth's sound. However, Macbeth sounds best to me with either the Eletech "Sonnet of Adam" cable or if you can swing it, the Eletech "Ambition" cable that is a custom-built IEM cable just for Macbeth in an effort to bring out Macbeth's absolute best sound. I personally believe Sonnet of Adam is a perfect middle ground in terms of sound quality improvements and pricing. It provides roughly 60-70% of what "Ambition" does, but for $1,300 cheaper. What I hear when listening to the stock cable and SOA cables back-to-back is that SOA enhances the Vocals by making them a little more present, it improves the clarity, the tonality, and the soundstage characteristics. I believe it considerably improves upon Macbeth's treble presence and it's resolution by giving it stronger detail retrieval abilities. This alone is impressive given how much detail retrieval Macbeth already has with just the stock cable. The primary areas of clarity improvement I felt were in the high-mids to treble regions. The timbre produced with the stock cable is already TOTL, but I think SOA improves it even further.
In the end, Macbeth will truly be "the" special and unique pair of flagship IEMs to have for the foreseeable future. You can check out user experiences for Macbeth along with in-depth user reviews by respected forum members on the head-fi.org website. Lastly, Your Mileage May Vary, and this is just a personal opinion of my experience with my pair of Macbeth IEMs.
Thanks!