I found a used Linn Majik Kontrol pre at a very attractive price.

The associated Majik power amp is not powerful enough to drive my B&W 703's so I was wondering if I could pair it with something else.

Check the specs on your proposed replacement amp and see if it has similar specs to the Majic amp. Pay particular attention to input sensitivity for full rated output . . . usually given in Volts or better, Vrms.