You should look up "Joe's Tube Lore" over on the AudioAsylum FAQ. He's goes into great detail on the 6DJ8 family of tubes. I have found his observations to be reliable. For a warmer sound you could try an early '70s Siemens 7308. They aren't as pricey as early CCa versions and would give you a taste of the 'Siemens' sound; warm, larger images, softer focus.