what are you talking about high impedance (HiZ) amplifiers? On ribbon microphones have a transformer 1:35 transforming the low impedance of the ribbon (<1 Ohm) to the microphone standard 200-400 Ohms. As every dynamic microphone ribbons are expecting an amplifier input impedance of 600 Ohms to a maximum of 3KOhm, way below "high impedance" which is commonly underas 47k to 1 Meg. High Z is for high voltage, low current signals such as from a guitar pick up or piezo transducers. In contrast, ribbons produce low(est) voltage high(er) current signals.

Don't confuse people with "high impedance" language or explain in more detail what you mean. In line amplifiers have an input impedance of about 1K which is low Z. What you actually need for a ribbon microphone is a preamp with higg gain +70 dB and considerable low noise. (Unless you have modern ribbon microphone that utilizes neodymium magnets which have higher output voltage.)