My Quad 510 monoblock power amps. They will drive any load between 4 and 100 Ohms, and being transformer coupled (both on the input as well as the output), one can 'stack' up to ten amps together in various series/parallel combination to supply up to 1,000 Watts. The input is fully balanced, with adjustable sensitivity.
As to versatile preamplifiers, well I guess that would have to be a Quad 44. It has five inputs whose sensitivity (both input and output levels) and equalisation can be changed through changing plug in circuit boards and through DIP switch settings, as well as a versitile set of filter functions in both roll-off point and slope. The 'Tilt' control is useful, when used judiciously and in small amounts, to correct for either an overbright or a 'dull' recording. All of the frequency adjustment controls can be switched out of the circuit if they are not needed. And it has a stereo/mono switch which I like to use when playing mono records. I don't use it much as I prefer to use a Mark Levinson preamp which has fully dual-differential balanced inputs and outputs, although as far as functions are concerned it is less versatile than the Quad, but it has a better sound performance.