I had stacked 57's and drove them with the 30 watt Atmasphere,and the MP3 pre amp.
Great sound, I regret moving on, should have had the speakers upgraded.
I also used a 1961 Bell tubed(6V6)15 watt integrated that was very close to the Atmasphere's,hence the reason for moving on.
Were the speakers not revealing enough of the difference between the cheap Bell and the Atmasphere?
Either way, both amps were magic on the stacked Quads, however flawed they were.
Find yourself a nice tube power amp and enjoy.