50 wpc is optimum to drive the Quads with a max of 100wpc after which, even at decent listening levels, the self protection kicks in and the speakers shut off. You may have experienced something similar. IOWs a tube amp with modest output, say 50 wpc, is the way to go. Am driving my 2905s with a CJ LP70S power amp running on 6550 C winged tubes. Even a relatively low 70 wpc tends to drive the Quads to shut down. My limited listening exposure with SS amps was a bit of a let down eg Arcam etc There is a natural synergy between tubes and ESLs but off course a lot depends on your musical preferences etc
Best of luck.
Best of luck.