Question for Mr Harley in regards to my Cambridge DAC.

I'm directing this question to Mr.Harley because he has heard and recommended the cambridge 840c often but anybody is welcome to comment. Here's the situation... I'm finally planning to get a laptop to play some downloaded music.  My 840c has a digital input s/p dif or optical that can act as a stand alone DAC.  What i'm wondering is how good is the dac (analog Devices AD1955)in the 840c comparing with some of today's dac?  Will my sound actually improved if i were to link the laptop to my 840c  with a usb to s/p dif converter? Should i just get a new DAC also?  How high should i go to make sure my sound i not diminished? 
In case your wondering i plan on getting a mac laptop and add pure music and link it with the MF v-link or the new Hegel HD2.  My present system also include the cambridge 840v2 and sonus faber Liuto.   Any serious comment is welcomed!