Dear @chrisoshea ; That gentleman that pass away was a tube lover and this and no other is the reason of his " fondness for SUT ", the SUT down there is a mustto have a necessity a " bad " necessity.
@lewm stop to wondering and solve it, in the mid time common sense is just common sense an a good response at least for me. Not for you? then solve it ! !
Btw, 300khz is an exceptional case, normally good SUTs goes to 60khz-100khz like LOMC cartridges and MM too.
R.