I received the new Ypsilon S2 and Epsilon R1 a few days ago, finally found the time last night to assemble them and have a good listen.
The Ypsilon S2 is a clear improvement over its predecessor, bass goes deeper and with more impact, highs have more sparkle but are never fatiguing, midrange kept much of their character, meaning very open and involving but at the same time they sound easier on the ears.
The Epsilon R1 compared to the Ypsilon S2 have some added qualities, better focus, midrange naturalness and leading edge definition, while adding resolution they don't sound brighter or edgy, bass is tighter, faster and with better definition.
I have to add though, that these differences are not a night and day situation and you need a good quality amplifier to set them apart, connected to a FiiO E07K the Epsilon S2 sounds 90% like the Epsilon R1 but when connected to the Violectric or Benchmark the differences are more distinguish and the Epsilon S2 sounds 70-80% like the Epsilon R1, hope that makes sense.
FWIW, the Epsilon R1 gave me the best sound I have heard in a Grado-ish design to date, remarkable.
On another note, while these are clearly tuned with L-Cushions in mind I have found the larger G-Cushions to work well, don't even bother with flats.