what's interesting to me (and something that i've come to realize over the last couple of years after auditioning a few current integrated amps, such as the anthem 225, the marantz pm 8004,and the cambridge audio 651-A), is that the headphone output section in these newer amps left me disappointed. compared with the h/p out from an amp 20-30 years old!
i took the trouble to audition all three of the above amps the same way: took my rotel rcd-1520 cdp, three or four cd's which contained music that i was very familiar with (played a couple tunes off of each cd, listening carefully to certain sections of certain songs (which could have been bass-light, or bass heavy or sibilant-sounding or a bit distorted or whatever. i used these cd's as "test" records).
i remember taking my grado rs1-i headphones (admittedly "colored" / "warm" on bottom, and an overall "bright" headphone in the upper registers). if i were to do this again, i would've taken my 701's (a much more "neutral" h/p, but my thinking at the time was: "if this amp can't reproduce the bass and upper-midrange through these grados, then i know it won't through the 701's."
were there differences between these amps? to quote sarah palin: "you betcha!"
most people would probably be surprised to hear how different just these three amps sounded from each other (with everything else in the listening chain being equal, even down to the interconnects, and even the song order that i listened to the cd's every time out).
the first guy at the shop where i listened to the anthem (very nice piece of gear, by the way and seemed to be very well-made. a quality piece). but, he said after i had told him that "this amp just sounds a bit too polite. way too polite for my taste. detail, yes. absolutely. but, not much impact at all. "distant" sounding (on a "foreward-sounding" headphone!). very, very refined-sounding. but just a bit too refined-sounding". he said: "you know, this amp will sound much better through a quality set of loudspeakers."
well, i do most of my listening through headphones, plus anthem made a point in their advertising to point out the "separate headphone amp circuit" engineered into this amp. i'm not technically-minded, and certainly not an audio engineer, so i wouldn't understand exactly how they implemented the h/p out into this amp even if they explained it to me, probably. but, what encouraged me was seeing as how they devoted space in their advertising to go into some detail about the headphone output, period. "ah! the h/p out is not just an afterthought in this amp. the engineers were thinking about it from the beginning." i was encouraged. then, i listened, and found the output to be "anemic" sounding.
if anthem had allowed more (current output?), and then maybe incorporated a "high-low" switch to go from a higher-to-lower setting...in other words, if this integrated would've had more slam and "weight" (along with the impressive level of detail that i heard), then this piece would've definitely been a winner.
but... so it goes. i think, personally that the lack of good quality h/p outs in a lot of modern, mass-market audio gear explains why we started to see specialized companies making amps specifically designed for headphones.
and why we're seeing a return (among some of us) to older, vintage amps and receivers. (it doesn't hurt that a lot of the older gear looks good, either. but, she can't just be pretty, she's got to "put out", too).