when using analog lines you are limited to 2 external parties. But yes it would stand to reason that introducing analog trunks into a multiparty conference (presumably most parties on PRI?) would give the quality a hit.
I have a dream - where someday both sides of the atlantic will stand side by side, brothers, equal in the sight of both God and Avaya. Where both will be permitted to eat in the same restaurants, drink from the same water fountains, and both be allowed to use BRI trunk interface cards. When that great and glorious day comes, we shall throw OFF the chains of analog trunks that bind us and a GREAT CRY shall rise up from North America - Free at Last, Free at Last, thank God Almighty (and Avaya) we are FREE AT LAST!!
(little tongue in cheek there... *grin*)
Peter