I think you will find your solar regulator should regulate your solar charge once it senses your battery charger input .

I have my battery charger and solar /wind controller all wired into house and starter via VSR and once the battery's are full both inputs will go to float until I put load on battery's.

example : when I'm motoring and my alternator is charging the battery's and they are close to fully charged the solar imput will show zero. Once the engine is shut down and I start using a load the solar regulator kicks in and starts putting amps back into my battery's.

I had the D250 dual on my last yacht can't recall it was that expensive. I ended up removing my solar from the unit and hooking it direct to the battery as the five stage charger would take too long to charge my house battery's when disconected from shore power. I recall the first stage is like 3 amps or so for 6 hours....etc