Marantz HD-880 are excellent
I have a pair of HD-880's that I bought new about 30 years ago. Got them for half price ... $800 for the pair .. in 1970's dollars, of course, don't know what that would be in today's dollars .. thousands I suppose .. and today with mass production you get a lot more for the money, so the same quality doesn't cost that much more than 30 years go.
My HD-880's had the foam surround problem on the 12" drivers and I foolishly pulled and tossed the beautiful sturdy cast aluminum basket frame Marantz units and replaced them with steel frame $80 Radio Shack speakers that matched the resonant and similar stats and required the same port and cabinet volume. The RS drivers don't sound bad, but I kick myself monthly for tossing the originals.
I've worried about the dome tweeter and super tweeter thinking maybe the matrials in them have dried or aged and maybe they are no longer performing as well, or that today there is better technology. But, lots of people have listened to these things over the years and marvel at the sound ... and they were about the best you could buy in the 70's.
I just upgraded my amps to a pair of Adcom 555 mk II's (200 W rms into 8 ohms) with one pair driving a subwoofer and the other driving the Marantz HD-880's. The sound magnitude and volume are awesome. The HD-880's aren't complaining at all even on Enya played LOUD. The HD-880's go down to about 30 Hz but I roll them off at 60 Hz only because I have a pair of 15" drivers in a 12 cu fit box and in isobarik (two drivers face-to-face) that are down only 3 db at 20 Hz. Point is the advantage of the subwoofer is small with the HD-880's ... you gotta have one heck of a sub to make adding a subwoover worthwhile.
I've thought about replacing the drivers in my HD-880, but used an SPL meter to check sound output and the 880's are still flat as high as the meter will go (about 10 kHz) and probably beyond. I don't know what the tweeter dome material is, but I recently pushed on one (accidentally) and it sunk in and poped back out without damage (a dime size push on the 1.5" tweeter). The 5" mid driver looks to be in good shape as well with the rubber impregnated paper code edge still flexible.
You will pay a thousand or more, maybe much more, to get four-way speakers like these (four-way limits distortions that come from a driver handling two different frequencies at the same time).
If you decide not to do anything with these HD-880's, I would be very interested in acquiring the 12" drivers!!.
Harrison