Hi NewInTown,
Yes, the 20.5 will do very well. We have used the 20.6 (the upgraded version of the 20.5) for many years on our Extremas (has it been 6 already? *sheesh*). You won't have the finesse of a very high-end solidstate amp or the lush musicality of a very high-end tube amp (the Extremas will will love the best amplification you can afford to give them) - but the 20.5 have all the current you would ever want (more so than the Classe, as many others have tried Classe, like brunogolf above, even going so far as to try bi-amping, and were often not happy campers over the long term).
Enjoy!
Mike
Yes, the 20.5 will do very well. We have used the 20.6 (the upgraded version of the 20.5) for many years on our Extremas (has it been 6 already? *sheesh*). You won't have the finesse of a very high-end solidstate amp or the lush musicality of a very high-end tube amp (the Extremas will will love the best amplification you can afford to give them) - but the 20.5 have all the current you would ever want (more so than the Classe, as many others have tried Classe, like brunogolf above, even going so far as to try bi-amping, and were often not happy campers over the long term).
Enjoy!
Mike