4-4 vs. 4,5,6 ---- split or double??

In a DAS game, when the TC gets "high", does one continue to split 4-4 vs 4,5, and 6, or does one double down? In PBJ, Appendix A, Wong has a note that says "With 4-4, splitting is better than doubling down only if doubling is allowed after splitting." Is he referring to BS, or to the indices? If he is referring to the indices, is he saying to treat 4-4 as a hard 8, and follow the index number for that?

As an example, say one has 4-4 and the dealer has 6, with TC = +10. The index number for 4-4 vs. 6 is -5, meaning that one splits when the TC is >= -5. The index number doubling for 8 vs. 6 is 2. So....do I split or double?

-- Thanks, Homer J.