You need to remove the grills and look at the surrounds or edges of all the round speakers for rot or they even could be missing. If so, all the speakers need to be "re-foamed" in order to be used. If you don’t want to tackle that, they would be part units and not worth much. Also for these to work correctly, they need the equalizer that came with them when new.
I looked up through the attic door and saw one of my wife's original series 901s. Still looks new. When the guy demoed them for her he actually plugged the speaker cable into an AC outlet for a minute, to show how TOUGH they were. No she didn't buy the one they plugged in. LOL
I'm sure they sound the same way they did 37 years ago when I put them up their.. Cloth surrounds.. and they are HEAVY.. Still have the original stands too, somewhere.. The EQ is JUNK. 2 Hung HIGH and 2 stand mounts with super tweets and subs.. Pretty good for the time and a GIRL..
She use to complain about greasing the stupid bearing on her Garrard, it DRIPPED into a catch can it was her Dads.... LOL
Yesterday she moved the speaker in the front room AGAIN.. YUP he will move a speaker.. BUT she tapes first to move it back.. Hers, Mine TAPE. LOL
you can get a mini dsp(precurved for the bose speakers) that can replace the Bose original eq for $189.00us that can help old ones sound good again,and it will have enough outputs to add a sub with the one cable
makes my series IV ones sing,that and 400 watts rms per channel
a huge sound stage for a small size speaker