poweramp tube matching

Newbee, I recently read an article on the very point you raised, namely

"when each tube can be individually biased doesn't that overcome the problem you bring up?"

And the author explained why it doesn't compensate for the tube's not matching. I'll try and remember where I saw it ;--)

Power tubes need to be matched for gain (transconductance or gm) as well as for current and both are equally important. Individual biasing does in effect match up tubes for current output, but it does not address gain. For that, you have to match the tubes as well. Also, even with individual biasing, it's better if a pair of tubes are in the same ball park for current ourput as well. My own rule of thumb, with individual biasing, is to match tubes within 3% for gm and 6% for current.

what about tubes in input stage, do they have to match?

Re small tubes. Not IMHO in an unbalanced design. Same brand, same type, and with NOS I'd probably be looking for same vintage as well, so both (or more) have the same tone. I use this criteria for pre-amps and other tube devises, except for phono stages where I would use closely matched pairs. FWIW.