Use the index numbers
> Using the ao2 system the general index to double 8 vs 6 is tc +5.
> For single deck games standard basic strategy says double 8 vs 6.
> Does this mean always double 8 vs 6 or do you still use the index
> number for the single deck?
Since you know the correct index number, use it. If the TC is below +5 don't double down. The reason basic strategy tells you to double down is because the composition of the hand usually sends the count close to +5.
For example, off the top of the deck a hand of 4,4 vs 6 will have a RC of +5. Similarly, a hand of 5,3 vs 6 will have a RC of +4. A hand of 2,2,3 vs 6 will also have a RC of +4. As you can see, because the hand is made up of small cards the count will generally be high enough to double down.
However, basic strategy is not always correct. You may be dealt those cards and still have a negative count from the previous round(s). That is why we use index numbers to adjust our play. Although basic strategy is corect in an "overall" sense, index plays will be more correct for each individual situation.
-Sonny-