Can't help you with SR325i, but reading a lot about the similarity of Grado sound throughout their line, my experience below with SR80i might help.
I have been using SR80i for about 3 months now and I simply love them. I don't think SR80i are bright or aggressive or shrill (maybe SR325i are - can't comment on that). I play mostly FLAC 16/44, 24/96 and use them with Audiolab Q-DAC, however, even when I use them directly off an iphone or a laptop, shrillness or aggressiveness is not how I would define the sound. Indeed, vocal, jazz, rock, classical, ambient electronic (genres i primarily listen to) sound amazing - the best I have heard compared to similarly priced closed headphones. Grado's have a very tight and lean bass (which I think is closer to reality). The lack of boomy unnatural bass may give a perception of forwardness to some. If you want bass in spades - these are not for you.
SR80i's ear cushions are not uncomfortable and i can easily keep them on for a couple of hours. Although the comfort factor is not their strength. SR325i have a different design so can't say if this holds for them.
I am a firm believer of using high quality (irrespective of price) electronics for headphone use also and despite popular belief, I think Grado's, although efficient, sound better through the DAC/HPA than direct. If that is true for SR80i, it would be certainly true for SR325i.