I’m thinking of acquiring an O2 with gain settings of 2.5x/6.0x. Or, these settings will be overkill with my ath-ad900x. So I want to get a 1.0x/2.5x gain settings that would be more appropriate for me. And I found this picture. http://www.jdslabs.com/pdf/O2_LowGain.pdf So if I understand well, I have to cut these two resistors and it will become 2.5x/1.0x (so the “low” position would be 2.5x and the “hign” position would be 1.0x). Am I right?
Yes, you are correct. With those headphones I would do the 1x/2.5x option. If you order from us, just place a note on your order and we'll do it for free.