Early Audio Research (SP6 series, SP8) are famous for their classic sound and their superb phono sections. Conrad Johnsons from this same period were more "tubey" sounding which comes through well on the solid state amps. But plan to buy in-line gain-reducers for these preamps, as they pretty much all had high output voltages compared to more recent transistor gear. Thus you may overload the amp, or at the very least will have the volume control turned down so low that it is barely usuable.