what can I get by with?

What can you lose by trying them? As stated: It all depends on your room size and the volume you require to be happy.

Why ? So many always wanting to try SET but not with the right loudspeakers to go with a SET. Your just asking for disapointment. Even kt88 845 SET wouldnt run your 86db loudspeakers.Sure they will make music but your not going to hear what a proper SET based system would do. So if you want to try SET get a loudspeaker designed to run off SETs. If you dont want to change loudspeakers get a PP tube amp. Its not just power or volume level a SET will react to impedance of loudspeakers. Today hi-eff loudspeakers can come in many diferant designing including ribbons dynamics horns TL BR AS line arrays so much to pick from. Not just fullrange or vintage horns.

Well it appears I was wrong on the spec. The Kestrel ( mine are hotrod ) is 89db. Most of what I am able to find about the reviews of SET ask for at least 90db. So maybe I can get lucky if I can find a SET with at least 20 watts? I remember I once ran 60 watt amps through Vandersteen 3a speakers. Something that some dealers advised agianst. The bass wasn't much but oh the midrange!

To bad Meadowlark is out of business, they would have my answer.

Now that is possible with a good 15 watts, if the speakers are an easy 89 dB. I run 89 dB speakers with a 14 wpc SET. Room isn't huge and I've never heard my amplifier congest. The more you turn in up the more open it becomes. Just get a REAL SET amp you'll probably be fine. Down the road you can mate it with a higher efficiency speaker like John Ks and reap all the benefits.