The main differences are in the woofers. The 1 used an aluminum former for the voice-coil while the 2 used kapton, essentially a plastic. There are pros & cons to both, mainly the 2 will handle it better if the woofer is bottomed accidentally. There may be minor differences in the crossover because the response is different between the two woofers. The 1 woofer would have a bit better high-frequency extension, the advantage of the aluminum former.
About 6 months back I bought a set of mint 1's because I could not pass up the price. I did not listen to them for quite awhile and was never really a fan of the 2's. The layout of the speaker is good with 1" tweeter & 8" woofer but they just didn't sound all that great to me. I expected the same of the 1's and was surprised when I listened to them with a good amp. They sounded really good, /face palm. Either I heard the 2's in a crappy set-up or the minor differences of the 1's are audible.