Sounds cynical I know, but he is selling his latest BHK Preamplifier design through P.S. Audio. Why wouldn't he say this now, and not back then when he probably heard much better as well. This clip doesn't convince me one iota.
For the ultimate transparency and source signal transfer to the amp: Direct (source to amp) is best, if you don't "bit strip" with the digital domain VC, if it does, then 10kohm passive comes in a close second, so long as the impedance are matched, which 90% of system are matched.
But if your system is not quite right and needs to be coloured in some way, then a preamp with the "right" colouration can be fix for that, but good luck finding the "right" one. As none I know of, sound like a "straight wire with gain", they all sound different to each other.
Cheers George