Big flush w/Paired board

[Hair_of_the_Dog]

Live 3/6 Laggy (75% preflop raise & 20% raise/re-raise) table with an average of 5-6 seeing the flop

SB and BB are both new to the table and I've never seen them before. The have played 2-3 orbits and have played fairly tight (pucker factor 6 on a scale of 1-10 where 10 is water tight) for this table. They seem to know each other and have similar playing styles.

Hero on the button with A [img]/images/graemlins/heart.gif[/img] 2 [img]/images/graemlins/heart.gif[/img]

6 callers preflop
Flop 6sb [4 [img]/images/graemlins/club.gif[/img] K [img]/images/graemlins/heart.gif[/img] 9 [img]/images/graemlins/heart.gif[/img]]
Checked to MP who bets
HJ calls
Hero calls
1 other caller
Everone else folds

Turn 5bb [4 [img]/images/graemlins/club.gif[/img] K [img]/images/graemlins/heart.gif[/img] 9 [img]/images/graemlins/heart.gif[/img] 6 [img]/images/graemlins/heart.gif[/img]]
Early player bets
MP raise
HJ 3bet
Hero Cap
Early player folds
MP calls
HJ calls

River 19bb [4 [img]/images/graemlins/club.gif[/img] K [img]/images/graemlins/heart.gif[/img] 9 [img]/images/graemlins/heart.gif[/img] 6 [img]/images/graemlins/heart.gif[/img] K [img]/images/graemlins/diamond.gif[/img]]
MP checks
HJ checks
Hero ?