A lot of stuff is snake oil and then there are really good components for laboratory use. The problem for a lot of people that are not engineers is that they will focus
on one part in a circuit and neglect all the rest. If you are going to do changes to a good piece of equipment you need to be like Rupert Neve in his design method.
There is no sense using hyper precision audio grade resistors in a circuit with a $.35 op amp and regular 5% resistors as well. When you examine things from all angles, it is best to use such parts to design an amplifier or preamp section from scratch and you may end up with a very expensive device that does about the same thing as what was commercially available. Usually the cost/ results ratio goes way up in fighting for those last few percent of perfection.