Gundam91: I'll be doing an extensive test of Grado RA-1 headphone amp with the Grado RS-1s vs Sen 600, which I have on order from Germany.
I also have just purchased a Placette active line stage preamp, which contains a class A headphone amp. In a preliminary 2 hour A/B against the RA-1 (which in itself is a very, very good headphone amp) the Placette totaly smoked the Grado. Most pronounced, was "less jumbling" of complicated treble pieces -- the Vishay resistors really add nothing to the source and there is absoultely no distortion on the high end. To be fair to the Grado which costs about $325, the Placette retails for $4000.
The Placette is especially gradifying with SACD, XRCD and other high end recordings where there is little/no digital edge to contend with, as I do not have a DAC (source is an SCD-1). As I spend 50% of my time listening to headphones, I take this stuff very seriously, and my current setup is very close to some of the better STAX setups I have heard, including an older Omega I system. --Lorne