FSAF (Fast subband adaptive filtering) measurement

A dense multitone signal, like this 48 tone/oct one generated in REW, wouldn't be "broadband" enough?

No.

I'd suggest generating colored noise instead, with a spectrum similar to that of the music you like.

I'm a fan of M-Noise for general noise stimulus that resembles audio spectrum, a lot better than pink noise anyway. I think Stoneeh's trying to compare result of FSAF to a multitone IMD type of measurement, so needs to keep the magnitude spectrum and crest factor similar or it's not a very equal comparison.

The only reason for the existence of simplified tests like sine sweep and multi-tone IMD tests is their low computational load. Their interpretation in terms of music is ... debatable. Many self-proclaimed experts claim that by looking at FR, harmonics, and spinograms, they can predict how a loudspeaker will sound in a given room. Others call it snake oil.

FSAF comes from the opposite direction. It allows you to separate distortions from the original, on the music you listen to. Then you are free to come up with simplified tests that are consistent with your perception of the distortions that are meaningful to you (because each person is unique hearing-wise). Not vice versa.