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maybe you are talking about 37.5Z:600Z for solid state outputs?
QuadEight used to use things like these with some of their older discreet opamp. Pretty low primary impedance. What´s your problem? Low headroom? Why are you looking for such a stepup at the output?
Unless you are talkin about STEP DOWN, 10kZ:600Z, 4:1... For tube preamps?... Is that what you meant in the first place?