I've paired the Creek OBH- 21 with at set of Grado RS1 Headphones. I've actually started out with the OBH- 21 SE model, but paired with the Grado's I found that the SE model were too revealing. The sound were more analytical than musically, so I went back the the shop and traded it for the OBH-21 instead. The OBH-21 have a bit lower audio resolution than the 21-SE. It has a more linear sound and that works better with high resolution headphones, such as the Grado RS 1. It plays music, rater than dissect the sound on the recording. It works wonderfully in my setup, but I only give it four stars becouse it is a good headphone amp, but not high end. If you are looking for at good headphone amp to a reasonable price, and are not an audiophile, but just enjoys good music, you won't go wrong with the Creek Audio OBH-21