Design 2nd order sections IIR filter for high orders (more than 500)
The Schroeder/Moore implementation uses sparse IIR filters. It's extremely inefficient to implement these as regular IIR filters or biqauds. 

It's much easier and more efficient to implement these directly. See for example
https://ccrma.stanford.edu/~jos/pasp/Schroeder_Allpass_Sections.html

Both the comb filter and the schroeder allpass use the same structure as a regular IIR filter, but the delay(s) are not a single sample but much larger number. So the Schroeder allpass looks like any other 1rst order allpass except that the delay in there is big. If you want get technical about this 

The algorithm was specifically designed to be computational efficient, hence it makes no sense using standard biquads. On the downside, it typically doesn't sound very good. Feedback delay networks tend to sound a lot better.