LSA Voyager GAN Amplifier

With the 1K output impedance, 38K is a ratio of 38, and 100K is a ratio of 100, both way above 10, so I would expect the 38K and 100K to sound the same, as you found.  However, public demonstrations in unfamiliar systems are not as revealing as making changes in your own familiar system.  So ricevs' improvement in sound quality must be due mainly to the better quality resistor he is using in his mods compared to stock.  Let ricevs say whether I am correct or not.

You are both wrong.....he he....resistor types/brands can make as much difference as anything.....We found that out years ago with different brands of resistors loading our moving coil cartridge.....huge differences.

Same with impedance.  $150K sounded much better than 49K......both had the same brand and type of resistor.  The "better" brand of resistor was already superior to the stock resistor.  This is on the input of the amp (not a cartridge load.....we also liked 100 ohms for our Supex cartridges).

Here is an interesting story for all you measurement types.  Back in the 70s it was all a big club....everyone knew everyone.  High end was super small and few companies.  We knew David Fletcher who owned Sumiko (importer of Supex and Fidelity Research Cartridges)....in fact, we were in the same City (Berkeley, CA).  So, we borrowed 10 brand new Supex cartridges form Dave and mounted them on universal headshells and gave each one a number on a piece of small masking tape on the side of the cartridge.  Three of us listened all day on my system......All the cartridges came with frequency sweep graphs that told you nothing as they were so similar.  There were three categories of cartridges.....the meh ones....the OK ones and the great ones (three of them).....and one was clearly the winner..  This is how you learn to trust your hearing.  All three of us agreed with every ranking.....it was easy to hear.  I wonder if cartridges are as variable today as they were back in the 70s.   By the way, we did the same test with 5 Fidelity Research cartridges....maybe a year later.....mostly we preferred those to the Supex.

You are both wrong.....he he....resistor types/brands can make as much difference as anything.....

That was always going to be a given, doubt very much you could tell any difference between all the "known good branded" same value/wattage metal film resistors as an input loading resistor to ground.
Just like you say you can see many mods you can do to this amp to take it to another level just by looking at this photo, https://ibb.co/Dr86JY6

Of course, that is exactly where we heard the difference.......as a cartridge load to ground.   We all heard the difference in ALL brands and types of resistors.....still can, wherever they are used in a circuit. Tons of audio companies pick resistors for "sound".  It is true that most "metal film" resistors of the same type and wattage will sound similar.....but try a Caddock or Nude Vishay or various good sounding surface mount resistors.....and a way different sound emerges. 

Yeah, whatever Ric.