I own the SR80i, 325i and DT990-600ohm ~ of the three, the DT990 is my relax and chill, laid back can.
Perhaps it's because I'm used to the treble but I've never found the the DT990 to be aggressive in attack or sibilant
in it's treble, it is however quite punchy and quick when amped properly. Amping it properly is a challenge indeed,
it requires a +6dB gain switch on my Violectric V200 which is really saying something considering it's one of
the more powerful solid state amplifiers at any price.
Having said that, here's a brief run down of the differences :-
Grado 325i :-
First row presentation - practically sniffing the musicians on stage, attack is very prominent on just about
every note being played, bass impact is very substantial but it does not extend excessively, everything sounds quite
forward and the treble extends very nicely to the mid treble. Mids, mids ~ this can rules for that, again guitar
reproduction is the best I've heard ~ the LCD-2 and LCD-3 are very close to my ears but again the general Grado
tonality still gets the nod for me.
DT990-600 (100dB/sensitivity):-
Row 10 presentation - sitting further back, mids especially feel like they're coming from further back, nothing
ever seems too distanced though and it's never washed over by the bass or treble. Ahh the bass, it digs deep, for reggae,
electronica and other impact bass genres these are very good indeed with sub bass, reasonable impact but
extension is exemplary to my ears. Treble is very detailed and extended while never becoming harsh, the DT990
has shown me upper treble detail that was missed by the 325i. Sound stage width is much bigger however in terms
of sound stage depth ~ it's a close race between the 325i and DT990. It's a popular myth that Grados have no
soundstage, the width is not huge, there is no height but instruments appear out of the dark musical background
very nicely nonetheless.
They complement each other beautifully. Please note the DT990-250ohm is a different beast, it's more forward
and generally a little more sibilant and not as refined as the 600ohm. The big challenge is amping the 600-ohm.
As I said, when you find yourself flicking gain switches on a $1000 head amp, you get the idea of how demanding
this can really is to drive to 100% of what it can do.