I owned the MS2i and by all means it is a great sounding headphone but it just wasn't my taste. To me the MS2i and the (325is which I currently own) sound nothing like the RS1i. I also didn't think the MS2's sounded anything like the 325's. The MS2i's had a mi-bass that to me drowned out everything else, so to me there is no comparison between the MS2i and the RS1i, (they are just two different headphones IMO).
The SR80i IMO comes pretty close to sounding like the RS1i, but don't forget I still have to spend more time with the RS1i, I only got it last Thursday. So far compared to the 80i the RS1i has a little more bass, a slightly bigger soundstage and depth, and I hear a bit more subtle detail, but the higher frequencies to me so far can be a little fatiguing, and as of now they don't seem as crystal clear as my 80's.
Compared to the SR325is's it sounds to me like the 325's have a tighter bass and a much stronger, smoother, more powerful mid-range with vocals guitars and brass at higher volumes without being fatigued, ( slightly darker, more controlled) but the sound stage seems much narrower with the 325's at times as compared the the 80's and the RS1i's. Don't forget the 80's and the 325's have plenty of hours on them both, so these are just my initial impressions with the RS1i's so far.
Also last night I listened to the RS1i's out of my home system, Adcom-GFP-710 and Meridian-203dac and Sony CDP-C801ES and they sounded the best with these sources so far as compared to the MBP with the LD1+/Modi and the Magni/Modi. Both the 80 and the RS1i sound great out of my home system, yet the 325is's don't sound nearly as good out of my home system, but they sound great with the MBP, LD1+/Modi and the Magni/Modi... Go figure.
I can't wait for you to get your RS1's, so I can hear your impressions on them.
BTW, my 80's sound great out of all of my equipment, and I'm not saying the RS1i's had a problem with any of my equipment, they sounded best so far to me out of my home system, (much more controlled) especially with the higher frequencies.