Not sure that you are asking the right question. I think that the right question would be what solid state amplifiers would be a good sonic match, and avoid excessive brightness, with YOUR speakers.
The reason I say that is that in comparison with most tube amps, most solid state amps will tend towards brightness with those particular speakers, due to the interaction between their much lower output impedance and the impedance characteristics of the speakers, shown
here and
here. The Quad's huge impedance decrease that occurs as frequency increases, and the low impedance of the Maggies at high frequencies in comparison with its large impedance peak in the lower midrange, will cause an amplifier having low output impedance/high damping factor (such as most solid state amps) to sound brighter than one having higher output impedance/lower damping factor (such as most tube amps).
That said, back in the day the famous Mark Levinson HQD system paired his ML-2 pure Class A 25 watt amplifiers, having huge current capability, with the ESL-57 (and a separate woofer and high frequency tweeter). Perhaps the Pass XA30.5 would be a comparably suitable choice today. Some of the higher powered amps in the XA series, as were suggested above, may also be good choices, while perhaps also being better suited to the Maggies, but you would have to be careful to avoid overdriving and possibly damaging the Quads.
Regards,
-- Al
