http://tekmarcontrols.com/images/_liter ... 0_a_06.pdf
This document shows 6 different configurations for different piping arrangements and whether using Indirect water heater or not.
Some configurations use the 2 way, 3 way or 4 way mixing valves for these 24 volt floating action valves.
Lowering the boilers water temperature will effect the DHW output w/ a tankless coil, where as w/ an indirect DHW it will only take more time to recover.
With primary/secondary piping w/ normal boiler temps would not effect the DHW output.
There is yet another system which varies the speed of the injection pump with an injection controller instead of the mixing valves. (Tekmar 365)
Your specific piping arrangement will dictate what is most feasible.
If your answers you get here fall short, the folks at Pex Supply can get you on the right track.