As you know, I bought an MS2i at the same time you did. They are a great first Grado, and I can easily say they are the "sweet spot" in the sub-$300 Grado line up. Not nearly as bright as the 325i or 225, might even be called "rolled off", but this is a pleasant sound. Not as resolving as the RS-1, but they are still detailed and pretty airy for a Grado. The bass and the midrange is where it is at here. Marvelous! I'm loving listening to beat laden electronica, but even better, rock vinyl, since vinyl shows off those low frequencies so well. Also, the MS2i can be listened to at high volumes (relative to other, brighter Grados) for longer periods of time without being fatiguing. This also makes the bass that much more impactful and exciting.
As for pad choice, I think flats are definitely the way to go on this one. Bowls take some of the oomph out of the bass. I also have the reverse quarter mod "vwap" hd414s, and like you say, they exist in the land between bowls and flats. To be honest with you though, I've never been a huge fan of the vwap with any Grado, now the MS2i included. YMMV, of course, it may be worth picking up a pair just to have around, but flats have pretty much been the winner on all the Grados I've heard (GS1000 being the exception, bagels win here, and I've never heard the PS-1).
Glad you are enjoying the cans!