I am always amazed at the density of information in Griffin's
Theory of Blackjack.
1) Check out page 72. Griffin describes a method of adjusting the EOR column by 1/2 for 2-deck, or 1/4 for 4-deck. Then, the adjustment fraction changes to 103/(104-n) for 2-deck for example.
However, there are slight differences in the off-the-top or mean column for the various decks. While there's enough information in Griffin to estimate the appropriate adjustments, there's a better way.
Buy the latest paperback edition of
Blackjack Attack, available here. In Appendix D, you'll find complete EOR tables for 1,2,6 and 8 deck games, S17 & H17. It enhances Griffin's charts, and adds a 'mean' column for each of the various games mentioned.
2) Yes, it's the DAS/NDAS difference that causes the discrepancy. In single deck S17, hitting (4,4) vs 6 is 9.88% better than splitting if NDAS. If DAS is allowed, the decision flip-flops, and in a big way. With DAS, splitting is better by 7.35%.
(The difference between 9.88% and Griffin's 10.96% is I think because Griffin's mean column only removes the dealer 6, not the two 4s as well.)
Of course, doubling (4,4)v6 is better than hitting in both cases.
Bottom line: With (4,4)v6, split if DAS, otherwise double.