Whether you use PSS or QPSS (aka PDisto) depends on the frequencies you are using. Generally, the time required for PSS (like transient) depends strongly on the frequency ratios, but only weakly on the number of harmonics requested. Conversely, the time required for QPSS does not depend on the frequency ratios, but does depend strongly on the number of harmonics requested (except for harmonics of the clock, which like with PSS are largely free). Generally you want to use QPSS if the frequencies are such that either transient or PSS analyses will be really expensive.

There is a relatively new document in the Analysis section that attempts to lead people through a complete simulation of SC filter-like circuits. You can find it at http://www.designers-guide.com/Analysis/sc-filters.pdf.

Have you looked at it? If so, maybe you can describe where the explaination it gives is lacking.

August