How can I control 170 small 6V bulbs with MOSFET outputs (PWM dimming)

[zali]

There must be analog output controller or pwm controller for this job. Have you consider using ws2812 or equivalent LEDs for this job. You control 100s LEDs very easily.
Attached is example of stirlight where you only need 4 wires to control 100s or sets with few lines of code. You can however use kc board control on/off colour chang and intencity change if you will.

best regards
Zali