If you can find CV at Kuchai, they have been around for awhile and have happy customers. That same row has another 2 installers. Dunno anything about the middle 1, but the one furthest from CV, the boss seems like a nice guy. Suggest you go survey the 3 places 1st. Compare prices then see how.

If I'm not wrong, its here

http://wikimapia.org/#lat=3.09129&lon=101....992073/CV-Audio

Why 6X9? The installation price alone may not tell the whole story because extra costs may have been worked into the price of merchandise. You didn't survey the 3rd shop?