If you don't purchased your tubes yet try also 6CA7 (old EL34 US types) they sound fantastic on my orchestra reference. I personally like EL34's because have more wideband and much musical then KT90's. KT'90's are more broadband and punchy. It's a matter of taste. My opinion don't even try 6550. My best experience is on 6CA7.
I appreciate your experiences
Happy listenings
I appreciate your experiences
Happy listenings