It would be worthwhile to find out the vintage of the Tesla tubes and, if they will do the upgrade without them, what is their value.
It was suggested to me the pair of tubes that have the most impact on sound quality are those at the LV1 and V2 sockets.
You could experiment with that, if you haven't already, by using less expensive tubes in the other four pairs of 6DJ8 type sockets and save your premium tubes for the final output stage.
Rather than spend $900 on the SE upgrade, you might want to consider what I did. Put that money toward a Placette Passive and compare it in your own system. I purchased mine used and could easily sell it for what I paid. If you buy a new one, you get a trial period with no risk. The Passive replaced the Line 3 SE in my system and it's a keeper.
It was suggested to me the pair of tubes that have the most impact on sound quality are those at the LV1 and V2 sockets.
You could experiment with that, if you haven't already, by using less expensive tubes in the other four pairs of 6DJ8 type sockets and save your premium tubes for the final output stage.
Rather than spend $900 on the SE upgrade, you might want to consider what I did. Put that money toward a Placette Passive and compare it in your own system. I purchased mine used and could easily sell it for what I paid. If you buy a new one, you get a trial period with no risk. The Passive replaced the Line 3 SE in my system and it's a keeper.