I am in the process of making model 18 (620 cabinets) speakers using the drivers from a pair of Altec Model 938-8AD stage monitors. 1) How do the drivers and crossovers from the 938's differ from those of the Hi-fi-oriented Model 18's? (that is, the 604-8H)? Are the crossovers substantially different? Happy to have joined this group, thanks and best wishes.