Well unknowns here are the size of your home and energy efficiency of your insulation and windows. But if your oil burner worked fine, that K6 should kick ass and take names. I think you've lost something in your circulation system by valving off your oil burner. Also gotta go with Sting on the flow. If your return water temp from your zone(s) is not dropping you are not giving off energy to the radiation. I think you should make dinner, buy some really good beer and invite a half a dozen of us over for on onsite review. Oh BTW some of us will need plane tickets unless Greg can pick us up on the way in his Airbus.
I have to agree with coalkirk. Do yourself a favor and take a pad of paper, stand in front of you boilers and draw a one line diagarm your system. Show the location of all pumps, boilers, air separator, tees, valves, etc. It should be fairly simple but make it an accurate diagram as far as relationship of all components. Do not sketch from memory.
Scan that sketch in or take a photo of it an post it. Maybe we can see something that you may take for granted.