A quick google search pointed to this >> PCA9685 | NXP Semiconductors Datasheet and clearly shows this IC is for LED controllers.
I think you should share the Datasheet to the LED strips or atleast the link, because to me, it looks like the reason you were suggested the i2C port expander like chip to control the LEDs is because the strip is just LEDs standalone and nothing like a WS2801 Chip driver to control the RGB pinouts on each of those RGB leds on board the strip!