Hd250 Linear 2 is completely different headphone than Linear 1 in terms of distance and softness of mids and timbre. I got from what I can tell 600 Ohm Linear 1 and late 600 Ohm Linear 2 (with grey rings). Mids on Linear 1 are placed further away in a distance, and the overall sound is more delicate and less hard sounding. Linear 2 has lost the unique placement of sounds in a distance and everything with them sounds placed in one distance. Linear 1 does mirracles because of that unique placement and softer highs. It also sounds I guess colder which gives the sound interesting timbre. Linear 1 has lower amount of bass slam, less aggresive sound. It tells story of a song. Linear 2s have just those unique flaws erased and all this uniqueness had been repaired, plus the tuning matches better with the “ideal sound” (a bit more bass, slam, harder sounding notes ). But because of that it lost the miraculous sound character. While I like Linear 2, Linear 1 has more soul. Also worth noting is that I like it with several amps (shanling m0 portable, r2r11) but I am not sure if I like Linear 1 particurally with Chord Mojo. While it sounds better amped and clearer, gone is that unique sound of underpowered headphone that Shanling M0 gives it. Linear 1 and Linear 2 sounds closer to each other with Mojo. Well it is not that bad, but Shanling M0 gives it some kind of underpowered flavour that sounds very interesting. So linear 1, not linear 2 is my choice. And pads: wang_yifei’s pleather pads from eb.. give it more of much needed bass and ensure a good seal and keep the treble and mids intacted. And if you want to enjoy more of its amazing highs on some recordings, get replacement Sennheiser pads for HD430 from Thomann. Velour pads (Sennheiser replacement velour pads for Hd560 from Thomann) do not give it a good seal and I do not recommend those.
/edit - yes, I like Linear 1 with Mojo as well. But I recommend to you to learn about the sound of Linear 1 from less powerful sources first to understand what Mojo does to it and where it does something against it.