After some cursory research I've found the following two quotes. The first, from Wikiepdia, likely has other sources in the footnotes, but I didn't look. Honestly, I found it really hard to read your post and not view it as incredibly racist.
The study found that "(a) putative genetic racial differences do not account for a major portion of the IQ performance difference between racial groups, and (b) black and interracial children reared in the culture of the tests and the schools perform as well as other adopted children in similar families." [0]
"This paper proposes a parsimonious alternative explanation: the apparent IQ advantage of East Asian adoptees is an artifact caused by ignoring the Flynn effect and adoption’s beneficial effect on IQ, and most of the IQ disadvantage of Black adoptees disappears when one allows for attrition in the Minnesota Transracial Adoption Study, and acknowledges the results of other studies. Diagnosing these artifacts suggests a nil hypothesis: East Asian, White, and Black adoptees raised in the same environment would have similar IQs, hinting at a minimal role for genes in racial IQ differences." [1]
Looking at the first study you point to, I'm not sure why that is the stated conclusion. If you look at the data charts... well, as the article says later: "Both Levin[8] and Lynn [9] argued that the data clearly support a hereditarian alternative: that the mean IQ scores and school achievement of each group reflected their degree of African ancestry. For all measures, the children with two black parents scored lower than the children with one black and white parent, who in turn scored lower than the adopted children with two white parents. Both omitted discussion of Asian adoptees." On the Flynn-corrected chart, the age-17 IQ respective numbers are 83.7, 93.2, and 101.5.
But then there are further arguments and counterarguments; the "Interpretations" section is a full page. One coauthor says, "The results of the transracial adoption study can be used to support either a genetic difference hypothesis or an environmental difference one (because the children have visible African ancestry)." That's not true because "The adopting parents of 12 of the interracial children wrongly believed that their adopted children had two black parents", which at least gives you a comparison point for fully back vs. mixed, but that point is also disputable because "The study showed significant differences in adoption patterns of mixed-race black/white and black adopted children as was noted by Scarr and Weinberg" ("Children with two black parents were significantly older at adoption, had been in the adoptive home a shorter time, and had experienced a greater number of preadoption placements. The natural parents of the black/black group also averaged a year less of education than those of the black/white group...").
It would be nice if people identified the genes responsible for the main visible differences between races, verified that they only affected skin color and maybe a few other cosmetic traits, and were able to manipulate that directly to do controlled experiments. (And to confound actual racists by hiding someone's true race; having a lot of people with randomized racial appearance seems to be the most thorough way to train everyone to not make judgments based on apparent race.) Who knows when that'll happen, though.
