oponent runs 31/17/5. should i be blocking this river? villian has a PS stack infront of him... what kind of line is optimal here?

Full Tilt No-Limit Hold'em, $0.25 BB (5 handed) Full-Tilt Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP ($26.85)
Button ($25)
Hero ($41.40)
BB ($25.30)
UTG ($19.40)

Preflop: Hero is SB with 8, 8.
1 fold, MP calls $0.25, 1 fold, Hero raises to $1.35, 1 fold, MP calls $1.

Flop: ($2.85) 9, 7, 6 (2 players)
Hero bets $2.25, MP calls $2.25.

Turn: ($7.35) 2 (2 players)
Hero bets $5.75, MP calls $5.75.

River: ($18.85) 9 (2 players)
Hero ?