To be honest I'm not a fan of the way this hand is played at all. Now to be fair I'm not 6Max player so maybe you should take what I say with a grain of salt but here is my reasoning...
Preflop - maybe calling a bet with A9 suited is okay on the button however once its re-raised you really have to think you are beat and I would be folding this every single time.
Flop - you flopped top pair with a medium kicker and a flush draw. Pretty good for your hand but there is a real chance you are still behind. At the moment it is only a medium strength hand and I don't feel like you need to be betting in a situation like this. The risk of being check raised by one of the others is too great IMO and it puts you in a tough situation. Check the pot and keep it small.
Turn - you got raised all-in...worst case nightmare really. Chances are you are beat at this point.Lets look at this rationally. What could the CO have? Could he have a hand worse than you. Could he be bluffing
with complete air on with a weaker ace. I doubt it is complete air as he would be unlikely to call a re-raiser with a blind steal attempt....Weaker ace....possible.....but does a weak ace ever check-raise the turn here? Doubtful. Could he be semi bluffing? Other than your diamond draw there are only gutshots out there. Once again I would consider this doubtful. Is ever going to make this play with KK's? Once again, doubt it. So more likely he has the goods now and believes that you will call.
So it is a reasonable assumption we are going to have to improve here to win. What he has will determine how many outs we have to make our hand. There are basically 3 types of hands here.
Best Case Scenario : AK or AJ. Along with our flush outs we have the 9 of clubs and spades as outs as well giving us a total of 11 outs. Another 2 or A would give us a split pot. So 13 cards in all to avoid complete disaster. This is probably the most likely scenario given that he flatted the raise preflop rather than 4betting.
Not so good Scenario : AQ. Hitting our 9's are no longer good. We must rely on our nine flush outs to win this pot. A 2 will give us a split pot but an ace is no longer good so 10 outs to avoid complete disaster. Once again AQ falls in the realms of possibility of his preflop range.
Oh dear God Scenario : AA or QQ. To both these hands we are basically drawing dead (drawing to an Ace with the QQ). They have a full-house and our flush is no longer good. I doubt he has either of these hands as the typical 10NL player would re-raise all in pre-flop with this kind of hand but its certainly more possible than a complete bluff IMO.
So lets assume the best case scenario. We have 11 outs to make the best hand. Using the 4 / 2 rule, since we are calling an all in bet we times our outs by 2 to get the percentage of times we will hit. 11x2 so we have 22% to win. Now his all in bet puts us all-in for about half the pot. In this best case scenario is this a good call? No it is not. With a half bet call on the turn, we need to be at approximately 25% to win any money on this in the long term. Making this call will lose money even in the best case scenario that you have 11 outs, let alone in cases where you are actually drawing dead.
Fold it and don't look back