I have a Benchmark HPA4 and use it to power Kennerton Rognir Planar, RAAL SR-1b, and JM Audio Editions XTC-Closed phones. I previously had a Quicksilver headphone amp but found it just a little too warm and bass-prominent with these phones so the BM is just right for me--fast, detailed, transparent, and spacious. I tend to like that type of sound versus phones these days that are entirely too bass-prominent and dark. Maybe that is because I grew up when phones and speakers didn't have the overhyped bass that are everywhere nowadays. I posit that we have become conditioned to bass-heavy music. The BM also has a line stage that can power other amps.
