I be impressed with this little Nuforce HDP both as a dac and as a headphone amplifier ; which be high praise from someone who own a $ 15,000 headphone rig with stax sr-007 , sennheiser he60 and hd800 headphone , a Woo WES amp , Eddie Current ZDT amp , and PS Audio Perfectwave DAC . the hdp seem to offer a lot of performance in a small package , and easily outperform my original Nuforce Icon amp that I buy May 2008 for my computer desktop . and the beauty be that it be small enough that I can use the HDP 's superior dac to feed the original icon when I want to listen to speaker -lrb- both amp be the same size -rrb- . the feature list be quite full , include 24\/96 bit rate usb and 3.5 mm 24\/96 optical input , 24\/192 coax input , rca or 3.5 mm analog input , 1\/4 '' headphone output , and variable output level rca preamp out . not many dac in this price range offer 24 bit\/96 khz sampling rate , and even my 2x more costly Apogee mini-dac only do 24\/48 via usb . the hdp use 24\/96 usb input from my Macbook beat all my other $ 100 - $ 500 usb dac\/amps in the house , and even beat the headphone output of my Apogee mini-dac with usb . the HDP 's RCA line-out seem almost equivalent to the Apogee 's 1\/8 '' line-out as well , where the Apogee seem to be a little more refined sound at time -lrb- if use my upgrade Sigma 11 power supply -rrb- . the hdp be very detailed and transparent , with good sense of air and space , and offer a deeper soundstage than the Apogee headphone out . the HDP bass have great extension and impact , with rich mid and sparkly crisp treble . and it be just a little to the warm side of neutral , so I can still enjoy it with brighter headphone like my hd800 or head-direct he-5 . likewise it be also a good match for my hd600 headphone and my re-cabled Denon d7000 which can sound darker on the wrong amp . some amplifier that be good with full-size headphone may not be a good match with very sensitive in ear monitor -lrb- aka earphones or IEM -rrb- , and they might have noise , or hiss that be not otherwise detectable with full-size phone . well , that be not a problem here . I find the hdp to be a excellent match with all my very sensitive universal and custom mold in ear monitor , include monster turbine pro gold , westone 2 , Westone 3 , Westone ES3X , Ultimate Ears 11Pro and JH Audio 13Pro . it do a very good job with all of they , despite they widely vary sound signature . the ue11pro can sometimes be bass heavy or have some recessed midrange with the wrong amp ; but neither of these be a problem with the HDP , even though it be not a bass-lite or forward sound amplifier . how they manage to squeeze such good sound into a price this low be unclear to I , because you basically have to spend $ 700 - $ 900 for a better dac -lrb- Apogee or Stello -rrb- and $ 700 - $ 1,000 for a better amp -lrb- upgrade Woo WA6 or ALO Amphora -rrb- , and you would have to buy both a dac and amp to get most of the feature of the HDP . -lrb- except for analog input for ipod or other player , where many DAC 's do not include those -rrb- . I will conclude by mention a couple of issue that I have . the hdp sound very good with a wide variety of headphone , but it might not be optimal with all of they . with my head-direct HiFiMan he-5 and Grado HF-2 , if I try to play those headphone at very high volume level -lrb- closer to max -rrb- then the sound can get a little strident and fatiguing in the high . I have hear this same thing with the he-5 and a $ 700 Grahm Slee Solo SRG II , and that be probably because the he-5 be very difficult to drive low impedance headphone and require a lot of current . with the he-5 headphone this happen at volume level that be much higher than my Woo WA6 tube amp can hope to achieve , so if I never try to play the hdp louder than my wa6 I would not have hear this . the Grado hf-2 can be a little boost in the upper mid and lower treble , and they just seem to respond better to my tube amp to tone they down a notch when try to play they at very loud level -lrb- level that would be damaging or harmful for more than a few minute -rrb- . at normal to moderately loud level this be never a issue . another issue be that the volume pot can have some channel imbalance at the very low end of the volume control when use very sensitive in ear monitor which do not require turn up the volume knob very much . this be common with most lower price gear when use IEM , but can be alleviate by turn down the computer system volume if you be use the usb input . however , none of these issue would prevent I from highly recommend this product . it make I eager to think about try they high-end product at some point .