What is the purpose of these passive high and low pass filters with this audio DAC which already has internal filtering?
According to  CS4334 datasheet, internal filter is good down to -50 -60dB only. Apparently, to meet the advertised 88/96dB noise level, a bit of extra low-pass filtering is required.

The capacitor is not "variable", it is a normal symbol for an electrolytic polarized capacitor. 

The Rload, I think, is a generic test load of a headphone. This tiny detail should not be much of concern.