Speaker Effeciency and Bass Production

You will probably need about 20 watts with those 89db speakers. The rule of thumb is that your speakers should be able to produce 101db at 1meter with the amp that you will use, and 89db speakers will require 16 watts to do that. But it is only a rule of thumb and other factors can come into play such as- size of istening room, and how complex the crossovers are in your speakers (complex crossovers can eat up power) and what type of music you listen to (orchastra music will require more power than simple music with few instruments playing) and lastly, how loud you like your music to be. For single ended try a 845 output tube (Antique Sound Labs makes a descent one) if your thinking about OTL call Ralph at Atmosphere and ask him what he thinks and don't forget Transedent Sound OTL amps.

Really, probably pretty expensive?

Atmasphere, I was curious and so I just viewed the MA-3 monoblocks which as you said can deliver 500 Watts. An amazing piece of hardware, it looks bigger than my furnace.

Thanks Racamuti. I believe the crossovers in the main speakers (Opera Quinta) are relatively simple, and I am doing the crossover between the subs and main speakers in the digital domain (using a Tact 2.2XP). I listen to a range of music, but singer-songwriter music is what I listen to most. I do also enjoy the occasional 100db+ blast of a good rock or classical tune, but it is more the exception. The room is fairly large, but I sit only about 10 feet from the main speakers. I had been considering the ASL amp (as mentioned in an earlier post). The little ASL Wave 20's have been the most reliable tube amps that I have had, and have not even needed a tube change in over two years of 10 hours per day use in an office system.