I've been using my 10yr old HD600's more than ever since I picked up a Fiio E12 + L9 cable (for under $140!). I use it with my 160 GB iPod classic that has close to 6000 songs on it. The cable bypasses the pods amp resulting in a very clean and powerful sound. The amp also has a 1-click subtle but effective bass boosting switch that I always leave on. This little amp is slightly larger than my phone. This is why, between the portability, song selection, and sound quality, I've been using my cans more than ever!
