Don't sell your speakers. Those are unique. However, they, like most Altec home furniture cabinets, suffer from a choked bass and a clipped upper end. The cabinets are just too small for the 15 inch bass drivers. And there are two of them in each of these cabinets. You could swap the 803A (I'm assuming it's an A) for 416s through, which might help the bottom end. Great Plains Audio sells them.
There are lots of great compression drivers that go much higher than Altec compression drivers, too, but I don't think that's your problem. My guess is old capacitors and inductors with a low crossover point. FWIW, I use BMS compression drivers in my Valencias (a truly underachieving cabinet design), along with a modded crossover and much more substantial internal cabinet bracing. I've no problems, but then a lot of Altec fans would burn me at the stake for what I've done. On the other hand, my speakers sound great with my turntable.
As mentioned, you're going to need some power to push those drivers and the crossover. Perhaps you could spend a little money and try biamping with an active crossover?
There are lots of great compression drivers that go much higher than Altec compression drivers, too, but I don't think that's your problem. My guess is old capacitors and inductors with a low crossover point. FWIW, I use BMS compression drivers in my Valencias (a truly underachieving cabinet design), along with a modded crossover and much more substantial internal cabinet bracing. I've no problems, but then a lot of Altec fans would burn me at the stake for what I've done. On the other hand, my speakers sound great with my turntable.
As mentioned, you're going to need some power to push those drivers and the crossover. Perhaps you could spend a little money and try biamping with an active crossover?