I think the pico amp/dac suggestion is quite a good one at your price point. The g-lite/pico dac is also a good suggestion but in reality may not be a huge step-up from the pico amp/dac. A bigger step-up, but at a larger cost is to go with the TTVJ Fet-A as the amp with the Pico DAC. IMO the Fet-A loves grados and sounds quite nice with the hf-2, at least with my relatively short audition at CanJam.