I used to work in a dealer when the original 753s came out and like a few people at the time, wondered what all the fuss was about. I'm even more confused now they have 'classic' status.
Their most notable quality was their excellent CNC cabinets which through their revolutionary use of smaller drivers were one of the first designs to employ a narrow front profile compensated for by cabinet depth. They were the first lifestyle speaker, before the term had been invented. This did give them an excellent soundstage width and resolution of horizontal positioning. I would add that it's unlikely that a pair of 753s would ever fall apart - that cabinet is as solid as they come.
They are a 2 and a 1/2 way design with the cabinet dived between the top pair of mid-bass and bottom pair of bass drivers. So, if you divide the cabinet in half and because there are two drivers in each half, divide the cabinet in half again, you can see that each driver effectively addresses a not very large volume of cabinet. As such, the bass response of the 753s is much more akin to a standmount of one 1/4 the size. Because they use four drivers, they do go very loud*, but in practice, they went no deeper than the 751 standmount of the same era which was the actual sweet spot in the 75x range.
The original tweeter (I can't comment on the latter variant) was a shocker and again was at it's best in the 751 which was small enough to be driven by the likes of Musical Fidelity A1s and various valve amps all of which had a rolled off treble response which didn't expose the tweeter's nasties. These sorts of pairings could sound quite exceptional if you liked your sound more euphoric than accurrate.
Incidentally, we had to replace many a mid-bass/bass driver in 753s as their looks tended to attract mutton heads with no mechanical sympathy, but who were determined to screw bass out of them using their 'tone' controls. Bearing in mind that these were a £600+ loudspeaker, we used to get invoiced for the mid/bass drivers at £11.99 each. Even in 1992, that was a dirt cheap driver. Bear in mind that a pair of ATC SCM-20 standmounts only cost £100 more, would actually go louder and deeper and yet cost £130 for the mid bass driver. That said, we never had to replace any. Not one.
I said it then and I'll say it now, there have always been better speakers for whatever is being asked then or now. People would come in, listen and ask to hear a similar priced alternative. We'd put on the massively better Ruark Talisman IIs and to a man, they'd admit it. Still, we sold bucket loads simply because the looked the mutts and WHF said they were good.
I suppose it depends how much you can find a pair for, but like a number of 'classics', it's frequently more than they are worth - I've seen pairs going for £500, which is ridiculous. As things stand, mundane speakers like MA RS6s will show them a clean pair of heals in almost every department and personally, I don't think the MAs close to the best in their class either.
Russell
*As such, they're quite well suited to modern AV amps which have power well beyond the amps contempary to the 753s and can employ a subwoofer to replace the disappointing bottom end. In this mode, they will work quite well, but you are hamstrung by the quality of centre speaker to match them. The question still remains why you would go to the trouble with modern designs sporting far, far more capable and refined tweeters.