Ralph is product (his active preamp) protection mode, omitting the reason behind a "why" the "rare" times a passive "may not" be the least coloured, least distorted, and best dynamically
Only when there is a impedance mismatch which is maybe 5% of the time, when the ratio is lower than 1:10
As most sources can easily drive a 10k passive, and a 10k passive can easily drive power amps that are 33k or higher input impedance, most are, the industry standard 47k and most tubes are 100k.
Only some silly Class-D are 10k input, passives don't suit these, as to many tube pre's don't either
Cheers George