2 school of thoughts.
1. One camp thinks all amps have a sound signature of their own (all amps sound differently). So to them, it is NOT BS. They truly believe all amps, preamps, DAC, AVR, AVP sound differently even with the EXACT SAME SETUP.
2. The other camp thinks amps, DAC, preamp’s don’t have sound signatures of their own. Only Processors (EQ, Tones, DSP) and different volume levels (not level matched) will sound differently. So they believe that with the SAME EXACT SETUP and Volume Level, amps, preamps, DAC should not sound differently if you don’t use any EQ/Tones/DSP.
You can read some free online archives of The Audio Critic. It’s an eye opener for many people.
There are other factors to consider besides the obvious COST.
1. Like Warranty period. Some are 1YR, some 2YR or 3YR or 5YR or 7YR or 20YR.
2. Also customer service during the warranty and AFTER WARRANTY.
3. With companies like Onkyo filing Bankruptcy periodically, will some of these companies last long enough?
4. Aesthetics and pride of ownership matter to a lot of people. So not just sound quality, but how they make you FEEL after spending $1K, $2K, $3K, etc. ?