Are matched tubes necessary

and if so at what level. I have a Sonic Frontiers Power 2 amplifier that uses 8 6550 or KT88 tubes. I can bias each tube individually, do I still need matched sets? If so, do I need/want octets, or is two matched quads sufficient?
Technically you do not 'need' matched tubes but as a pratical matter there is little down side as most dealers sell new production tubes matched. If you want to match tubes for your amp, a matched quad for each side is optimum. You just don't need an octet, it will provide you with no extra benefit and depending on available supply might be harder to obtain. If you buy spares buy matched pairs and replace both tubes in the curcuit in which the one tube failed.
Matching pairs is 'nuf if you can ID a complementary push-pull pairs. If you can't than ask Chris at