I think that's correct, you can tell by leaving the outside tubes out for a moment, if you have sound your correct (won't harm unit I do it to check when I forget). I read that all four tubes affect the sound, with expensive tubes I run two and two cheaper tubes. My Ray came with EH-6922 and a spare pair of Jan-Phillips, the Jan-Phillips were better sounding to me! Once I heard the fullness of Amperex 6922 tubes i could never go back the sound is that much richer. It is a little daunting at first, here's are some good reference;
https://www.tubeworld.com/6922.htm some descriptions of sounds
also for prices;
http://www.audiotubes.com/bjtubes.htm
general descriptions;
http://www.audioasylum.com/audio/faq/joes-tubes.html
hope these help!
