I would recommend a Woo 2 or a Decware CSP-2 as an upgrade, or a Schit Valhalla if you want something cheap. Both will make Sennheisers sing. I would avoid solid state.
I don't know much about the ASL headphone amps...but they never gathered much of a following on Head-fi, a sign that you can do better for the same or less money.
I don't know much about the ASL headphone amps...but they never gathered much of a following on Head-fi, a sign that you can do better for the same or less money.