You're all thinking deep inside the box.

You're fixated on "I have hot water, and I want hot air coming from my
airhandler, so I have to put hot water in my airhandler, how do I do
it?"

There's a better way.

You're making that hot air with a heat pump, which is extracting heat
from the surroundings. Put your hot water around your heat pump, and
it becomes much more efficient.

Then you have another benefit. Your ductwork and airhandler are
designed (if done correctly) for volume of air at a given
temperature. So the controls will still work and you won't short
cycle.

Then in the summer, when you're dumping excess heat from your heat
pump to cool the house, you dump some of that heat into your hot water
system. You get efficiency improvement year round.