The main thing I'm try to achieve is lower the noise floor of amps, preamps, etc. If I turn my amp way up (past 11 o'clock), especially with my low output MC cartridge on my turntable, I can hear a slight buzz.
Unfortunately, it's going to be near impossible for me to test out these before buying since I'm going to buy something second hand most likely. I do take your point that testing something in my system is the only way to determine if it's going to meet my goal.