add something into the signal path and the results are like the optomotrist says, same, better, or worse
its on us if we feel we should introduce a dedicated line stage between the source and amp.
I feel that decision is based on what I hear. usually, I'm looking for naturalness and organics. I also feel if that is not what is going on I should try to achieve it. usually this means adding tubes, IMO.
tube pre amps can alter and or enhance the sound cheaper than a very good solid stae preamp can. usually.
it does not mean one needs more than a single source to chase that goose.
its merely a matter of preffs and certainly just one more choice in this past time..