Speaker Effeciency and Bass Production

Good point!! It is a Vintage Conrad Johnson Premier 1, about 20 years old, but very good sound and power, 200 Watts per channel, which you aren't going to get with the SET/OTL. However, I was also using the same setup with a Rogue stereo 90 in Triode mode, which was about 40 watts per channel. The powered subwoofwer has a 175 Watt continuous amplifier and 475 Watts dynamic range.

Cyclonicman, there are OTLs that can make 500 watts, FWIW.

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.