Nordyne e2eb series furnace with heat pump

I have a 20 year old Nordyne e2eb series electric furnace. I rcently replaced my a/c with a heat pump. Everything works BUT when the Tstat calls for either heat or cool from the heat pump the blower fan activates on high speed. I have a Honeywell RTH6500wf series Tstat. The furnace does not have a control board. All it has is a 4-wire pigtail and an NO fan relay and an NC fan relay. The heat pump only has 5 terminals: Y, B, D (this poses another problem I'll get to in a minute), R, C. I assume that the reason the blower only comes on at high speed when the heat pump is running is because when the Tstat energizes the Y terminal it also enegizes the G terminal. And since all I have at the furnace is a green wire coming out of the pigtail, and there is no way for the furnace to know if the Tstat is calling for Heat or Cool, it is hardwired to run the blower on high speed either way. I can't figure out any way to fix this problem with what I have to work with other than manually switching the fan speed wires on the fan relay based on whether I am heating or cooling. plus, as mentioned earlier, without a D terminal on the furnace the HP has no way to call for aux heat when in defrost mode. I realize the Tstat will eventually call for aux heat once the room temp falls 2-3 degrees...
My question is: Is anyone out there familiar with the Nordyne P/N 902987 A/C Heat Pump (4-7 wire) Relay Box that is made for the e2eb furnace? And if so, will adding this option give me what I need to remedy my issues? Or will it still not solve the problems?
Or, is it possible to solve the fan speed issue by changing some wiring on the setup I currently have. (I do have a couple unused communication wires.) And can I solve the Defrost issue by running a wire from the D terminal at the HP to the white wire at the furnace pigtail? I already have a white wire from the Tstat Aux/Em Heat terminal to the white at furnace pigtail. That way the Aux Heat could be energized from EITHER the Tstat OR the HP. Does that work?? (That would also mean the D terminal on the HP would be energized any time the Tstat called for Aux/Em Heat. Is that a problem?Sorry this is so long. I've always found that if something can be said in 10 words or less, I need 500. Ha,ha! Or, is there a BETTER control board I can add to this furnace??