Outdoor Wood Boiler to Radiator System

[Oteys]

I have a 4500 sq ft 1850s farm house that I'm renovating. It has approximately 20 old cast iron radiators that were being heated by an Weil McLain propane boiler. I purchased an Earth Outdoor Boiler (505 Montain Man) to try to save on my gas bill. Last year spent $500 to $800 a month to keep the house on 50. I had trouble trying to find somebody to hook it up. Once I did, the guy by passed the old boiler in the basement and tied the hot supply coming from the wood boiler directly into the radiator loop and the return directly back to the stove and installed a larger pump that's tied into my thermostat and a check value to hold the water in the system. I'm eating through wood like crazy and it doesn't seem to be as efficient as I had hoped. Some guys have recommended putting in an water to water heat exchanger. The 70 plate exchanger has four ports so 2 would be in a loop from the wood boiler to the exchanger and back. While the other 2 would be looped into my radiator system. The guys I have talked to keep saying I have to direct it back through my old boiler. My question is why can't I just keep my old boiler separate since the larger pump I installed is controlled by my thermostat and would serve the same purpose? Am I missing something? And is this even going to help me out adding the heat exchanger? Thanks