Hope we're not hi-jacking this/ at least it jumps back up the list!
My memory slightly flawed; my Sandwiches are 15 ohm.
My 3090s-just looked - have a huge spec pasted on the back (200 watts music power!) that says Zt 5 ohm min, 10 ohm max 70Hz - 30kHz; Zt 15 ohm 15-70Hz.
(Must try that 15 Hz tone?)
I recall my Father, circa 1971, being advised to get the (2 unit) Sandwiches when he was replacing his Heathkit gear, as "they were better" (than the new 3 unit ones-600s?)
Those WERE 8 ohm (the Sandwiches) Should have kept them....too many things though?
Though, if the 600s came out earlier-I guess he could have got near-new ones; can't ask, he's listening to Angelic choirs and harps.
Chris.