Although not with the 325i, I spent some time with the new portable Pete Millet amp from TTVJ and the HF2 and 225, and found it to be a great match. I think with the dac it runs around $450, though, but I'm seriously considering getting one, not only due to how it sounds with my headphones, but the really slim size fits perfectly under an ipod touch, making it a great on-the-go set up when I want, and not bulky at all. It's something to consider.