Fast convolution with very high order FIR
you can split up your long impulse response into smaller segments and use multiple concurrent fast-convolutions that convolve each segment against your audio, align the delays correctly, and add up the result.

what must be the case for each segment (or one big segment if you don't split it up) is that if the FFT length is $N$ and the impulse response (or segment) length is $L$, the number of output samples you get for each frame is $N-L+1$.  that's the case whether it's overlap-add or overlap-save.  in either case, you pad your impulse response (or segment) with $N-L$ zeros (to bring it to length $N$) and FFT that.