DC coupling is good because you get rid of the low-pass filter, which even if it is below the audible range will still have a specific “sound”, as it will change the phase into the audible range. This is particularly true if you go through the filter many times, or through several filters. Also, the filter would also depend on capacitors which will have a variable capacitance with voltage/age/humidity/temperature, resulting in nonlinear responses. Avoiding the filter is better, many interfaces don’t do it because if you don’t know what you are plugging in, and if that has a large DC offset, then it’s bad for speakers. But here maybe SSL are confident about what gets sent to the interface, so may have gone with DC inputs? A small DC offset is really not an issue for speakers anyway, as the power goes with the square of the voltage, 10mV offset would be only 0.01^2/8ohm ~0.01mW, which will not affect speakers at all.
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