I wouldn't worry too much about heater current on our amps with double triodes. I used pairs of 0.3A+ tubes for months without issues (actually 0.3A heaters the minimum I would consider using for pentodes and single triodes, I often used 0.4 and 0.45A tubes, so a total of 0.9A), so 0.6 to 0.9A total driver heater current. The tubes we're looking at now have pretty petty heaters compared to what we've been using lol!
Interestingly, and despite the high gain of the 12AX7 tube I'm using, I find that the amp runs pretty cool compared to my previous standards. And that can't be a bad thing!
So, I guess we've reached a temporary conclusion on what to do with the shield on 6DJ8 tubes huh? Great, now I can get started on my soldering work.
Btw, I've just added a large amount of tubes of all types to my selling thread; just putting it out here in case someone's interested (there's a pretty large array of choices there lol).
http://www.head-fi.org/t/671097/little-dot-driver-tubes-ef95-ef92-ef91-more
There's also a thread below that one in the classifieds with my last DR supertubes; if anyone wants a "glory package" along with nice driver tubes... I might also have a MK IV SE unit for sale in a few weeks, if someone is looking for an even more glorious package lol. It's not mine, but my father's, who hasn't used it much apart from the preamp section and doesn't see the point of keeping it (so, it doesn't have loose driver sockets like mine does lol).