If you have read my CK100PRO unboxing impressions + previous CK series compilation review summary on Head-fi, I had personally mentioned under that review thread that for many of the BA driver CK line-up series models that I personally own, its pretty certain according to my ears I have encountered lotsa positive changes after hitting ard 150 - 300 hrs on them. The CK9 their 1st BA type model was one such example, during the first 100 hrs the overall sig of this phones was pretty dry and sibilant/peaky, but after reaching ard the 300 hrs mark the midrange and soundstage kinda opened up, mids texture got relatively smoother annd treble peakiness was slightly tamed. (it has ard the same kind of brightness as the CK10 model though the latter is still more liquid/refined in both mids/treble regions)
The CK100 (non-PRO ver) is also another one such example. Can find alot of examples on chinese community forums such as Mobile01/Erji.net where alot of fellow owners complained that the CK100 sounded relatively peaky or weirdly sibilant in terms of its overall signature traits during the beginning.
However those who have personally heard my CK100 before during last yr's Head-fi meet (and we had 1 guy who got deeply poisoned by my set and immediately went eBay to look for one, lols) would prob tell you otherwise in terms of their listening experience.
It is prob one of AT's most successful BA IEMs ever to grace on the market (at least in terms for HK/Taiwan/China market side) even when compared to the current IM series line-up, its overall signature after been properly burnt in has this liquid/smooth-sounding char with a very euphonic sounding traits (albeit coloured in a slightly warm sense) in terms of vocals rendition capability and with very decent soundstage/imaging properties as well. Upper-mids/treble properties is not as bright as CK10/CK100PRO/IM02 after proper burnt in, but has very good treble extension for a triple-driver BA. (can refer to Joker's review on Head-fi)
For my IM02, after proper burn-in sessions of ard 200 hrs +/- I also find that the bass quantity has improved, not so lean sounding anymore and soundstage details/dynamics has improved quite abit considerably. Not sure whether it's the cable that got burned in or the drivers themselves, but in my own words I would say burning in does apply to balanced armature based IEMs as well, just prob not as obvious/fast as compared to dynamic IEMs.
