Which driver are you actually using? 2404H or 2404H-1??

There is a significant difference. The 2404H-1 will tolerate a much lower crossover point but does not go up as high as a 2404H. The 2404H uses a 077 or 2405 diaphragm while the 2404H-1 uses a 075 or 2402 diaphragm.

The 4628B (and I believe the 4612B) contain a 2404H-1 and the network is designed for that driver. A 2404H will likely misbehave or die on that network.