Eliminate hiss and noise
You can use the DAC itself as the R part of the filter, and put a C from the DAC output to ground. The DAC appears as a 10k resistor.

What value of C? That depends on the highest frequency you want to generate.
I'm going to assume 3dB attenuation at 4kHz is OK, so R = 1/(2*pi*f*C) where R=10000, f=4000, solve for C. 

I get 4 nF.

(Incidentally the electrolytic cap C6 is shown wrong way round, + is connected to approx 0V)

I believe you also need to attenuate the input to the amp, it must be clipping at the moment. That attenuation will also reduce the hiss, and allow a second stage of filtering. For example, 20K in series with C6, 10K and 4nf in parallel from pin 3 to ground. Add this if the first filter isn't enough.