I think starting with 'what's the output of my 604's HF' is a better place to start.

Remember (or know), +3db = a doubleing of perceived volume (guys correct me if the terminology is not accurate).

So the 92db rated beston, is going to be half as loud at least as the 96db AC you initially post about. That's a big difference imo.

If the bestons are still viable, then they look cheap enough to play with. Otherwise investigate non-ribbons for other cheap options. Beyma CP09 (discon) /CP25 (more $), Piezo array...


Maybe instead, start with matching the new purchase's output (check the FR curve, make sure it's in the area you plan to use!) to that of the woofer, then just pad back the 604's horn accordingly (kind of a continuation of bowties suggestion).

For the 604 woofer section, you should be able to get nominally correct values, from it's companion. e.g. If a 604-k or l, probably matches the 515-8g series? So check the 515-8g for output spec'd in an alignment similar to yours (on horn in A7, or simple BR box, etc.)