Interesting, I personally own the SR60, SR325 and RS1, all of them older vintage versions, and I find the RS1 treble closer to that of the SR325 than the SR60 in terms of brightness, the SR60 having a treble closer to the amount of energy I prefer. I guess I should acquire a set of flats for the RS1 and see how I like it with them. And indeed the ATs and Grados are quite different, I only meant to compare them in my gut reactions to the quantity of treble as you move up and down each family.
I know what you mean about giving time to acclimate yourself to the IEMs. My own first impressions of the CK100PRO were also extremely positive in its amount of improvement in technical prowess over the CK10, while holding true to ATs' sound. Ultimately, I had hoped the CK100PRO would be able to handle anything I throw at it similar to how the CK10 was able to do that for me yesteryear, but I found it wasn't the case in it's treble. I had to make a cold rational decision to let them go. I would eventually like to find a suitable BA upgrade to the CK10 myself as the resolution these drivers are capable of are hard to give up once experienced. I wish you all the best with the CK100PRO, hope it works out!