One way to open lines towards his kingside is 8...d4. You're right about a6 being limp. It's WAY too passive. Have a look at Houdini's top ten moves in the position. No sign of a6.
you do have a sizeable advantage though and although opposite side castling when your opponent launches his pawns can be intimidating, allowing pawn to g5 has to be a mistake. I think the counter attack in the centre is the way to go as advice for such positions usually states. Good Luck.
Dear chess.com users one and all,
I just wrote a blog going into some detail about my thoughts as I played a game recently, where I was very frustrated at my inability to plan well, ultimately leading to a loss because I played without direction. The blog entry is here: http://www.chess.com/blog/john4000/planning-frustration
I'd be very grateful if anyone would take a look and offer up any suggestions for how I could have better assessed the situation. I'm pretty clear about where I went wrong, but what I'm more interested in is how could I have made the RIGHT moves instead?
Any thoughts very welcome.
John