Not sure if you are still seeking any input on this due to the dates noted, but there are a several good preamps with excellent headphone amps built in. I previously owned a Cary preamp that had a very good headphone amp, but I do not recall the model (it was an SLP). The benefit of this preamp was that if also provided for singled ended and balanced ins/outs and also had a HT passthrough or unit gain. I presently own a Melos Sha preamp/headphone amp. I purchased this to use as a headphone amp, but now also have it serving dual purpose as a preamp in a bedroom system. I am not sure about the output voltage and impedence though. It is an excellent headphone amp (I have a pair of excellent JVC Victor HP DX 1000 phones, the Sennheiser HD600, etomotyc research ER6i canal's and the new Westone 3's canal speakers. I haven't listened to this unit with the canal phones (as these are mostly portable designated) but the Melos does great with both the JVC's and the Senns. The drawback to the Melos is that is offers singled ended inputs and outputs only (no balanced connections) and does not have a remote control. But for a preamp, it is very good.