My Isos were unearthed when I moved recently.
It turns out I used a convenient Radio Shack speaker coupler, as you can see in the accompanying photos.
I plugged the provided 1/4" jack into my Schiit Magni 3 (don't remember there being a DIN plug) and they sounded great, just not very loud. With the volume control maxed out they could only go loud, not very loud or too loud.* I'll have to dig out an old amp of some kind to hook them into. If I had the $$ I'd buy a Schiit Aegir for them.
The sticker on the bottom of the case gives an approximate impedance of 120Ω and max input of 25v RMS. They also amusingly list the sensitivity as 30mW for 95dB spl. Listening Mac iTunes → Schiit Modi Multibit → Schiit Loki → Schiit Magni 3, the nominal output should be ~650mW into 120 ohms, and that's not enough. The Schiit Ragnarock, on the other hand, would probably drive them just fine at ~6W into 120Ω.
They still sound great. And that's not "great for their age", that's straight up great. With a touch of tweaking from the Loki I really enjoy these. As is common with open backs, they have a slightly more expansive soundstage than, say, my Beyerdynamic DT770s, but it's still all in your head. They're a little rolled off in the bottom end, but I suspect that might be due to the Magni's lack of power.
The plastic is yellowed from age, the ear pads are delaminating a little, but you don't notice any of that when they're on your head.
I'm glad I didn't get rid of these.
*These volumes are subjective, of course. Loud is loud enough for the 'phones to wake up and to listen to comfortably, but there's no margin for turning it up during quiet passages or to drown out external noises (they are open back, after all). Very loud is loud enough for rocking out in short bursts but not extended listening, and too loud is volume beyond comfort or safety. I do have a bit of hearing loss, about average for my seniority.
