I use these for audiophile listening (high, constant bitrate audio files) and live gigging IEMs in a professional band.I've waited a long time to write this review. I wanted to make sure burn-in had fully occurred so that I could compare them with my other IEMs. I have to say that I'm amazed by these units in this price bracket.When I first listened to them (pre burn-in) I thought there was too much bass response and not enough sonic balance. This is normal, apparently(?), and takes time to settle. Once they were properly burnt-in (around a fortnight of use) they balanced out incredibly. It was a night and day difference from brand new to standard use. I'm glad I waited 3 months to write this...I compared these to several IEMs. I also own a set of the Yinyoo KZ ZSX (1DD & 5BA drivers per unit) to compare them to, as well. The Yinyoo KZ ZSX are good IEMs with great reviews for a reason; there are very good. However, these KZ Zax units are even better! I also compared them to M6-Pro IEMs and other brands that I have. Across the board, these are the best IEM's I've ever used.The cable noise on the KZ ZSX was quite high. On the KZ Zax it's much better, with a much less noticeable cable noise.On the KZ ZSX units, one of the connectors on the driver unit had broken. I fixed it with superglue. This worked, but it meant I cannot remove the cable. So, I decided to get a new pair as I sometimes cable swap. I was going to order another set of KZ ZSX, but I saw these and took a chance on jumping up to 1DD and 7BA per unit. I'm glad I did.The presentation of KZ Zax soundscape is very even, exceptionally detailed and rich, without being overpowering in any frequency.In the beginning, prior to burn-in, the EQ on the bass was unacceptably high. You could hear the bass-guitar or deep cellos/double bass strings overpowering the rest of the music, as if the music had been mixed or mastered with too much bass. After burn-in the sound evens out over time. When these have reached equilibrium, the low middle, mid-middle, presence and treble matches the bass very well, to give unprecedented detail and richness to this listener's ears.The KZ Zax comfort is excellent, even better than the KZ ZSX units. While listening to music with the KZ Zax to music that I know very well, I have heard things I simply could not hear with the old KZ ZAX units.Yes, these KZ Zax units are £20 more than the very good KZ ZSX units. But, for those extra 4 Balanced Armatures, the more advanced audio tuning of the unit, and the clearly superior cable, it's well worth the investment.CABLE UPGRADE UPDATE: KZ Silver/Blue Hybrid (784 cores) Upgrade Cable. This is the best upgrade cable purchase I've ever made. I have upgraded the stock cable of my KZ Zax IEM and I cannot tell you what an improvement has been made! There's no cable noise at all and the sound is even better. The sound if full, deep, rich and more detailed, with a wonderful midrange and presence balance. I cannot recommend the purchase enough! However, there's a downside! There's so much copper in these cables that the volume you're used to will sound dropped as it's pushing against so much more copper. You have to up the volume output a lot from your device. This may impact battery time (device dependant) as you're pushing more energy through all that copper braid to have the same volume output.