I think and air exchanger will help immensely based on the change I see in pH when airing out my fishroom. The jump in pH is dramatic.
With some common sense, running your topoff through a kalk reactor isn't as risky as some people have been leading you to believe. Additionally, the Apex will notify you if things are going sideways. Your programming needs to provide some safety controls and some administration limits. If you are interested, I can post some suggested programming and tips.
When I tried it a couple years ago with a reactor it eventually blew kalk powder into the DT. My system can go through 2-4 gallons a day. I run a Tunze ATO. The only thing I don't like about it is every time the power cycles on it there a 40 second water dump. I guess they do that to be sure the lines are primed but I hate that there's no option to stop that behavior. Two other things I don't like about running kalk through an ATO for larger systems is the variances in Alk that happen due to the rates of evaporation. The other is if you mix it directly into your topoff water without a reactor you're putting the ATO pump at risk of failure, unless you're gravity feeding. Then the solenoid can corrode.
MY preferred way would be to use a reactor and dose with a dosing pump pushing into the reactor. Granted the type of tank someone is running plays a big part too. A LPS/Softy heavy tank with little to no SPS won't need to worry about Alk stability as much. Someone running an SPS or mixed reef that it heavier SPS would want more control of the Alk.
IMHO, do not chase numbers. If your tank is doing well with 7.8pH (as an example), than there is no reason to chase 8.3. Sometimes you might end up cause more harm than good. Good luck!
Also, some people may just want a nice tank to look at and aren't after faster growth. For them if the pH stays above 7.8 and the system is stable all is good.