How important is the cable between the SUT and phono pre?

looking at transformer equivalent circuits I don't see reflected capacitance.  Reflect impedance, reflected leakage inductance, but not capacitance.  Do you have cite for this?

@jpjones3318 Transformers are called that because they transform impedance. They do not isolate it!

So a load on the output of the transformer very much affects the source on the input side. This is part of why the transformer must be loaded correctly. Incorrect loading of the transformer can have other effects too- for example all transformers have inter-winding capacitance. If the transformer is too 'lightly loaded' (output load impedance is way too high) the inter-winding capacitance will begin to affect frequency response, perhaps manifesting as a hump in the frequency response rather than being flat.

Impedance != capacitance.  

MC step-up transformers explained

"The capacitance of the cable connecting an mc step-up transformer to the following phonostage also plays a part, which is why the interconnecting cable should be a low capacitance design and kept as short as is practical."

Hi @imhififan, he's basically explaining a zobel like I mention above, and some generic advice that may or may not fit a circumstance.   However, transformers do not reflect secondary load C to the primary.   

However, transformers do not reflect secondary load C to the primary.   

They absolutely do reflect any capacitance seen on the secondary by the turns ratio squared.  Say you have 150pf (50p cable + 100p input)  at the secondary of a 1:20 SUT.  This will appear as 150*20*20 or 60,000pF or 60nF or 0.06µF to the source.

dave