[quote user="Koonsism"]Is it worth investing in a good DAC in order to connect the Mac to a high end amp? Is it necessary to both get a DAC and a new soundcard or does the DAC do the same as a soundcard?[/quote]
You don't say which mac you have. Most macs have quite good built in sound so for no money outlay you can just use a 3.5 stereo jack to two phono lead, straight from the audio out on your mac to the line in on your hifi.
As combined dac/adc you could consider a Yamaha GO44 cost £65 or Edirol UA25 cost £140.
Either of the above will give excellent sound quality and many say they out-perform cd players in the hi end bracket such as Linn or Naim.
As another option many macs output optical s/pdif digital stream which can be fed into a separate dac of your choice such as a Beresford or Benchmark, but in my experience they are not better performers than the above choices and are unnecessarily expensive. Your mileage may vary.