There are now beryllium diaphragms available for some horns. They have less breakups and so sound smoother and faster. Crossover capacitors have improved as well. Throat and horn designs have improved due to Computer Aided Design, and so have less 'horn' artifact.
There are better coupling capacitors that are more transparent and smoother sounding- for example V-Cap Teflon.
It is possible to run balanced lines if you have a balanced line preamp. This helps prevent colorations due to interconnect cables, and might allow you to run shorter speaker cables, which can help impact and resolution.
There are simpler tube amplifier circuits that are also wider bandwidth and more transparent, with less IM distortion. So there are better things out there.
There are better coupling capacitors that are more transparent and smoother sounding- for example V-Cap Teflon.
It is possible to run balanced lines if you have a balanced line preamp. This helps prevent colorations due to interconnect cables, and might allow you to run shorter speaker cables, which can help impact and resolution.
There are simpler tube amplifier circuits that are also wider bandwidth and more transparent, with less IM distortion. So there are better things out there.