The SIN function will be the easiest.
It's what the FREQOUT statement uses to generate its sine waves.

It's essentially a pre-made lookup command. So it'll save you some work.
The result is an 8-bit number so you could just shift right twice and have your 6-bit value. But 8-bit would be better at such low frequencies.

You may also want to look at this from sirvo ...
http://www.picbasic.co.uk/forum/show...5843#post65843

I've pointed to the video of the finished project, but further up you can see how he did it.

It uses a lookup, and 10-bit PWM (with 8-bit values) instead of R2R.
I wish I had a scope like that.