That's a tough one, they're quite different IMO. The S2 has a warmer, thicker midrange with an elevated mid bass like the HD650. But unlike the 650, the S2's mids are not as forward. They sound farther back to me and just a bit compressed (in direct comparison, not in general). The 30's mids are more forward, more neutral, and clearer. Despite being more neutral, they're not boring. For vocals I'd take the 30 more often that the S2. The S2 is more engaging for drums and bass instruments. Overall if I had to pick one outright over the other just for the midrange, i'd go with the 30 for it's added presence/forwardness and clarity. I love the S2's added heft and warmth, but at times vocals sound just a bit distant and it bugs me. Fleetwood Mac is a great band I just do not like on the S2 compared to the 30. Stevie Nicks' velvety smooth and sensual voice comes through almost erotically on the 30, but on the S2 it sounds somewhat constricted and distant. Again, I don't think the S2's mids are recessed in general. But in direct comparison they just don't fare as well. But if you love visceral drumming and percussion, the S2 excels with speed, power and weight. When listening to Metallica's Death Magnetic, I prefer it on the S2 to the 30. Reason being that album has really dynamic and emotive drumming by Lars, and they mixed the vocals pretty forward, which actually makes them sound just right on the less forward S2. And those powerful drums on the S2 are pure energy. That album really resonates on the S2 like Fleetwood does on the 30. So you'd have to think on what's most important in a midrange to you. Percussive energy and drive or emotive vocals? Hope my drivel helps.
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