Very cool system, I too have the Senn HD 600, the Etymotic 4S and the Cardas Headphone cable. Instead of the cosmic, I have the supreme and for a CDP I have a Sony with a very good digital out. It really sounds great. I would recommend looking in other amps, maybe like a Meta 42 if you want the portability or a Musical Fidelity X-Cans for home. I really like the headroom stuff, but truthfully, it just is not as good as some other headphone amps out there like the MF, the Berning Micro ZOTL and the ASL MG Head. Good luck.
