As to the conversion factor for the Emerald, use the weight of a solid model x .9 to get the equivalent wax weight (Specific gravity of 1), then multiply by the SG of the metal to be used.
Have included a chart of metal SG I have been using for over 30 yrs., trust it. It is true that varing the different metals available for alloying gold to different Karats will cause the SG to vary a small amount. In the case of 22k you could use coins that are 22k or mix your own alloy with fine gold and use the following to determine the SG of the alloy.
Assuming 22k = 91.67% fine gold and the alloy is 5.33% copper. The resulting SG of that mix will be 17.7 to 17.8 (so the equivalent wax weight X the SG would be the amount of metal used to cast (not counting sprues and button).
Hope this helps.
Robert Howle
PS: A hollow print that is castable will not matter in direct casting as the investment only molds to the surface, therefore hollow prints or waxes should cast the same. I agree that a wax may be better for production work. I will print u good B9 resin print that u can used to mold for $35.00 (if i do 3-4 the price would be $25.00 each) + postage, if u need it. In most cases I ship the day following the order, in some cases the same day, just depends on my printing schedule at the time.
Robert Howle