[Note that the tape head version was discontinued a few years ago. We now offer only the RIAA version.]
The output impedance is around 4K-5K ohms IIRC.
While it is theoretically possible to make a switched set of different equalization networks, it is pretty complicated, and we never designed one. One would have to re-design the networks, and then find a place to locate the extra components and the switch. The area is pretty cramped, and the circuitry is sensitive to interfefence (hum and oscillation risk).
We did at one time make a tape-only version with a NAB/IEC switch, which changes only the LF time constant and is much simpler. It was something of a kludge and was abandoned about a decade ago.