Take some ideas from bs2b.

Bs2b uses the low-pass filter to generate the delay as a byproduct
of its operation. The filter is generally set around 700 Hz where
it produces about 250 microseconds of delay. In addition to that,
the crossfeed is now mixed at -6 dB level. The reverb is unchanged,
although the new configuration gives it larger role in forming
an impression of a soundstage.

The design is still not complete, but good enough for a commit.