I have owned the deHavilland GM70 50 watt S.E.T. monos for a couple of months now. I can't imagine ever needing to upgrade them. The music washes over me. Basses are tight and mids and highs are to die for. They are built 100% in the U.S.A. Tubes are easily replaced. They fill my room up(about 3600 cu. ft.) with Green Mountain Audio Continuum 3 speakers,with about a 90db efficiency. These folks will let you audition for 30 days in home (100% payment up front). I don't think anyone has returned them yet. Amp quest is over after hearing these.
Good luck. Tom
Good luck. Tom