Picked this beastie up from fleabay.... great value!
 
I happen to alread have an audiophile 24v PSU - the Creek OBH2 which I use with my Creek phono pre...
 
So I matched these together and started listening
 
I have no baseline for comparison yet, but it is driving my Revox 3100 (1986 Beyer DT880's) HP's very well, and making very nice sounds ..... Review and comparisons to come....
 
Update - the power supply makes a noticeable difference.... 

So listening to various discussions on Receivers and built in headphone jacks, with some people saying the resistor based HP Jacks are superior to the opamp based jacks - I thought I would put it to the test and ordered this little unit...
 
With the right cables (4xbanana to 1/4" TRS) this connects to the speaker output of a receiver, integrated or power amp and drives your headphones (up to 2 sets) directly.
 
It is simply a resistor network, including a passive resistor pot to adjust volume.
 
I also have a Firestone Audio Cute Curve to compare it to, which is powered by a Creek OBH2 power supply (so $400 ish worth of headamp)
 
The Headtap was connected to my Onkyo TX-SR876 Receiver, set to 4ohm (to reduce power output... no need for 140W into headphones!) and "Pure Audio" setting.
Source was my Media PC, with MAudio 2496 card playing FLAC files via SPDIF into the Onkyo
Headphones Used: Vintage Revox 3100 (Beyer DT880 600ohm OEM circa 1986)
 
The results of a few hours comparison is:
 
1) Both options sound really good (GF's comment... I could not respect someone who would obsess over such a tiny difference....and she is still with me...)
2) The Headtap has a sort of a slightly dry(er) sound with slightly forward mids, orchestras sound a little more distant, and the overall sound is a little less smooth (a touch tiring at times...) - has a hint of sound being listened to through a SS amplifier... Voice of a bass-baritone sounded like a deep tenor - lacked a little of the timbre  it should have
3) Cute Curve by comparison - Sound has more air, slightly more micro-detail, the bass is tighter, sometimes mistaken for less bass, but I think the bass is more accurate, feels more natural, unstrained, orchestras feel a little closer, individual notes seem to decay more slowly (naturally?), Voice of bass-baritone sounded very natural.
 
I do prefer the Cute Curve/OBH2 combo over the headtap ... clearly... but if I hadn't had them side by side, the Headtap was sounding very very good too.
 
Some further tests still to come include: Headtao vs Cute Curve (without OBH2), Headtap vs Onkyo internal Headamp Jack, Onkyo amp vs Quad 606 via Headtap - and if (as I expect) the Quad 606 beats the Onkyo, there would be a rematch between Quad 606/Headtap and Cute Curve/OBH2.
 
My observation of the Onkyo TX-SR876 sound into my speakers (Gallo ref 3.1) has a lot of similarities to my observation of the Onkyo sound through the Headtap.... and I prefer to use the Quad 606 power amp rather than the Receivers internal amps for that very reason.... (smoother sound, less tiring, more micro detail.. etc...)
 
Other people who have tried DIY resistor network boxes like this one, have made the comment that the sound signature of the different amps was even more obvious through headphones. (who would have guessed...)
 
This is fantastic value - if you have a good amp / receiver / integrated, and the HP jack is subpar (or has trouble driving your hard to drive / inefficient HP's) - then this is a very economical solution, which just happens to sound great too.

Thought it great until I recently comparered its analog out to the DAC on my Onkyo TX-SR876 receiver...
 
Although good to a point, it failed in highly complex loud music passages like the Choral movement of Beethoven's 9th Symphony..... where as the volume and the number of instruments and voices increased, the 2496 could not keep the sounds seperate.... they become muddled/mixed a little muddy.
 
Under all other conditions, and especially with Jazz, small acoustic, baroque music, there was no discernible difference between the two.
 
This is a great sound card..... but perhaps reaching the limits of what can be achieved internally within a PC