How are you hearing no difference?

As a new audiophile I find that any number of tweaks and improvements suggested make no appreciable difference to me.....while others make big differences. Speaker position for me is one of those things I notice right away. Small changes. Even head position can make a difference for me.

And then there are differences that I can perceive but have a hard time saying which is better. To me that is the real hard thing. And it also makes me wonder if different but equal SQ doesn't suck some people into constant changes and 'upgrades' which might only actually be lateral moves???

Listening with just your ears does not eliminate the effects of psychoacoustics.

You have to ask yourself, what makes them different.  For example obvious SS vs tube sound.  Then what are the caps and resistors used.  Power supplies.  I have mentioned this many times, the Counterpoint line is an example, the basic preamps use 1 6DJ8 tube, the next model up 1 6DJ8 per channel, then as you go up the line separate power supplies, tube regulation and tube rectification, so you get the picture.  If you are comparing similar designed components then they may not sound exactly alike but maybe not that different also.  Again tube vs. SS sounds, Class A and D designs, OTL and DHT designs, see where this is going?  If you only compare preamps that use 6922/6DJ8 tubes with similar designs, they may sound different but maybe not as much of a change that one may be looking for.  Probably better trying a 6SN7 preamp to see what that would sound like in ones system, etc.

Then there are people who can change the sound of a component with modifications, that can be as simple as better power supply caps, swapping out resistors with Vishay, caddock, shinkoh, swapping out other capacitors with V-Caps, Jupiters, Duelands.  And then there is adding filter chokes, upgrading transformers, etc.  These simple changes may change the sound to more what you are looking for, plus once you hear what these changes accomplish, this can then help you understand each design and what changes make a component sound the way it does in comparison..

Happy Listening. 

+1 to tomcarr.  Everyone hears differently, listens for different things or perhaps not as critically.