One of my friends does this:
mixer
electronic kit, plugged into mixer
keyboards, ditto
bass amp, DI'd into mixer
guitars, also straight into mixer
vocal mike, into mixer (no PA)
Behringer 6 channel headphone amp and 6 sets of cans
Not quite a silent practise, but just the acoustic volume of the vocals as far as the outside world is concerned. Seems to work - they've had no complaints and it would be a stony-hearted council indeed that would put a noise prohibition notice on one bloke singing! Unless it was Bono, of course.