I listened to the HPA4 at Axpona this year while auditioning headphones. I now have an HPA4 in my home system, as it paired astonishingly well with the Audeze headphones. It is dead quiet and just gets out of the way. Great bass extension and clarity. I got it to be my headphone amp, but it also ended up taking the place of my tube preamp (in front of 300b monoblocks). The tube pre has a little more bloom and spatial sound to it, but you really have to pay attention to notice. What was more apparent to me was the absence of a subtle distortion in the tube preamp that I did not know was there until the HPA4 did not manifest that same distortion.
Get it with the remote control - it is absolutely worth the extra $100 at that point.
Get it with the remote control - it is absolutely worth the extra $100 at that point.