I can tell you that the amp sounds VERY nice with the current version of Louis' 8" non-alnico hemp drivers, it will drive them louder than you want to listen, at least in my small room on OB. Unfortunately I can't comment on the headphone out, I will tell you that I tried to use the USB in, but couldn't listen to it very long and ended up plugging my Bolder modded SB3 back in.
Best,
Ed