Soundlab speakers...how reliable?

Soundlab is the one of the best-sounding, least reliable speakers I've heard.
This was true of the A-1s, anyway. High humidity could cause them to arc, burning holes in the panels. They were J Gordon Holt's reference speaker, though.
If you live somewhat arid, though, I say, go for it. They are a good match for OTL amps like yours. Why? I don't know. The results are good, anyway.

Also, you should visit the SoundLab Owners Group (SLOG) website to read what others have said.

Since the introduction of the 'PX' models about 6 years ago, the reliability issues of the older panels have gone away. The improved rigidity of the cores, stability of the stator wiring, and improved insulation of the stators has almost completely eliminated the failures that used to be common. Very few of the newer panels have had to go back to the factory for 'refurbishment'. Additionally, the latest improvement, the Toroid II transformers have improved performance considerably. If were considering used panels, I would insist on getting the PX generation products, and would upgrade to the Toroid II if they didn't already have it. (Disclosure: I am a SoundLab dealer.)