Have you considered that it may not be the amp? I know there are differences between the models, but in my SF Line 1 replacing the stock tubes with NOS 7308s changed the sound from similar to what you describe (I called it dry and somewhat brittle) to palpable and lush, though not to the point of being syrupy. It is not what I equate to a "tubey", but it is certainly less sterile and analytical than the stock sound.
It was also not necessary to use NOS tubes in all the sockets. Replacing the pair in the rearmost bank (final gain stage?) had 95% of the effect of replacing them all. At first I had Amperex World Globes in all three banks. Later, hearing about the "rear bank only" approach I replaced the two forward pairs with Sovteks. There was very little change. That this worked so well was important from an expense perspective as it allowed using better tubes without going broke in the process. Let's not even get into the problem of finding a quantity of a particular NOS tube!
If this is old news to you please accept my apology for burning bandwidth. In any case, good luck in finding a solution.
It was also not necessary to use NOS tubes in all the sockets. Replacing the pair in the rearmost bank (final gain stage?) had 95% of the effect of replacing them all. At first I had Amperex World Globes in all three banks. Later, hearing about the "rear bank only" approach I replaced the two forward pairs with Sovteks. There was very little change. That this worked so well was important from an expense perspective as it allowed using better tubes without going broke in the process. Let's not even get into the problem of finding a quantity of a particular NOS tube!
If this is old news to you please accept my apology for burning bandwidth. In any case, good luck in finding a solution.