I love my UM2s and the sound sig in general is really enjoyable to me, but I've been reading about possible upgrades, and I find the SM64 looks really interesting. Descriptions I read of the SM3 a while back made me really curious and these are apparently more well-loved. However, some reviews have made it sound as though it's lacking the warmth and bass that come with the UM2, but I'm not sure if that's true or not. It's a higher class of monitor, so those reviews might be comparing it to its peers. Everything does make it sound as though it has an overall better sound.
So anyone have an opinion on what a UM2 fan would think of the SM64?