A random revelation:
This nomograph shows why the lesser slew rate (6.4 V/ms) of the OPA209s that are used in the 2Stepdance causes no degradation of sound quality relative to the higher slew rate (27.0 V/ms) of the OPA1611s that are used in the original Stepdance. (This does not take into account any characteristics other than slew rate that distinguish the OPA209 and OPA1611.)
This should dispel any concern about the lower slew rate of the 2Stepdance OPA209s.
For more characteristics that distinguish the op-amps used in the 2Stepdance (OPA209) and the Stepdance (OPA1611), see their datasheets: