The bass of the 325i is good. Out from a high-end Denon CD player headphone out, it beat a pair of D2000 that were right out of the box - so much, in fact, that I found the D2000 lacking. But that could be just the set-up. The deepest bass I tried was Bach's Toccata and Fuge out of a church organ.
I have tried test tones with MacBook Pro + 325i, and the first tone I can hear as a tone is 15Hz, but it's not very strong. The sound joins normality somewhere between 30Hz and 40Hz out of the laptop. I haven't compared test tones with a proper amp, but my impression is that while the mid bass is indeed excellent: strong and very well controlled, these are not the headphones you pick for deep bass.