[Elecraft] K4HD switchable?

[Andy Durbin]

"> Can the superhet option be switched in/out independently for each of the K4D receivers?

In theory."

Why is this theoretical?  My interest in the question is for use with WSJT-X modes where I currently use a 4 kHz - 5 kHz RX bandwidth.  My understanding of the superhet spec is that it would be limited to about 2.8 kHz bandwidth.  

What is the max bandwidth of the superhet module and, if limited to 2.8 kHz, can it be switch out of circuit?

Thanks and 73,
Andy k3wyc