I have had these speakers from 1994, powered from Arcam Delta amps 290 (£400) / 290p (£380). They have served me well, they are at their best power driven. At various times I have tried to replace them but nothing bettered them under £1500. With HD music becoming more affordable, I feel the mission could be helped by a subwoofer 20hz to 70hz.
I have recently replaced the delta 290 amp with Arcam FMJ A28 amp £950, there was no sound improvement that shows how good the Arcam delta series were.
These speakers look amazing and the build quality is excellent. The top 2 drivers do all the work, the bottom 2 are passive bass units.
In my experience I found these speakers to sound a little "boxy". They don't breathe natural tones and sound a little restrained in the mid range. Also, because the drive units are only fairly small (only 130mm diameter) they can't really produce the gut thumping bass that you might expect.
These speakers need some real muscle to drive them correctly. Don't go sticking a 40W integrated amp behind them for example because they are very power hungry and you won't hear them at their best. With an impedance of 6 Ohms and sensitivity of 90dB you'll need something a little stronger to make these speakers sing.
One final note. If you are looking to buy some of these I would strongly recommend the 753f (Freedom) version. This upgrade replaces the metal tweeter with a nylon one which produces a much smoother, less harsh sound and makes for a more relaxed and enjoyable listen.