I used a late 70’s or early 80’s 3020 as a headphone amp for a few days.It was the original 3020, not the the 3020i though. If they kept the same wiring scheme you’re good to go, sounds real nice with phones but YMMV depending on impedance load with this modestly powered unit. With a hefty load you will likely not be able to push it up that far before the anti-clipping circuitry kicks in and drops the voltage. I don’t remember which phones I used on it, it was like 15 years ago but I’m quite sure their impedance was fairly low because I played them pretty loud, loud enough for me in any case. SQ was typical 70’s, real nice, detailed and even.It’s not the kind of amp where voltage drops dramatically when transients demand current.