Grumble Grumble Grumble
It's too late...The dub is already out with a Upgrade program in effect...
Section23's Clannad Dub Upgrade, Cast Detailed - Anime News Network:Section23 Films has provided more details on its Clannad Upgrade Program for early DVD customers who want the new English dub. Interested customers must send back the original, English-subtitle-only Clannad Collection 1 and 2 sets with US$20 (plus US$3/C$6 for postage). Customers who only bought one of the earlier sets can send back just that one set with US$35 (plus US$3/C$6 for postage). The upgrade offer lasts from April 1 to July 31.
Clannad: Complete Collection (DVD) - Anime News Network: