Not sure what Quads are referred to, but I have always been perfectly happy with mine (first ESL57s, now 2805s) driven by first a Q303 and now a Q606-2 solid state amplifier. I have also had the privilege of being given a private comparative demonstration by Quad's Peter Walker himself, at the time when people started to argue that his earlier valve amplifier sounded better than his later solid state designs, and in particular better than the Q405 current dumper. He thought all this was absolute nonsense, and commissioned an independent research project by James Moir: http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistor...
As I said, he gave me a private demonstration with a blind setup with his three designs, playing master tapes on a professional recorder. The comparison was level matched and blind. I thought I could just about hear slight differences, but afterwards Peter smiled: my identifications had not been better than random. All three amplifiers had simply been straight wires with gain; the only relevant difference had been that each successive generation had been more powerful than the previous one. I had learned a useful lesson.
As I said, he gave me a private demonstration with a blind setup with his three designs, playing master tapes on a professional recorder. The comparison was level matched and blind. I thought I could just about hear slight differences, but afterwards Peter smiled: my identifications had not been better than random. All three amplifiers had simply been straight wires with gain; the only relevant difference had been that each successive generation had been more powerful than the previous one. I had learned a useful lesson.