Benefits of DAC & Transport vs. CD player

the advantage of separates is flexibility. you can still find current production dacs using 16 bit, non up sampling chips. it is very difficult to find a one box player which does not up sample and uses a 16 bit dac chip.

you may be able to voice your source using two after market ac cords and a digital cables, insetad of one ac cord.

the advantage of a cd player, especially if it is tube-based is the possibility of finding applications for non-6 volt tubes. although many dacs and cd players in production use 6 volt tubes, there arev some cd players which take 12 volt tubes. i know of one dac which takes a 12 volt tube, namely the exemplar dac.

I own or have owned separate dac's, transports and CDP's.
Some suggest that separates sound better than a single CDP, and in some cases that is true. I have found that it all depends on the individual quality of each manufacturer product.
To make a blanket statement that is a generalization would be a mistake.
A single player does take up less space with one less interconnects, and visa-versa.

I agree with Lak's comments, you can't generalize because it all depends on what combo you are comparing with what cd player. Right now I use an Acurus ACD-11 as my transport as a lot of time and expense was put into that unit's air dampening system to reduce the effects of vibration and in turn jitter. The technology on the electronics side is now a little dated and so I run it with a DAC to for instance decode HDCD recordings. It is likely that if I upgraded to a current single CD player such as the Cambridge Audio 840c I would hear a sonic improvement but it would come at a monetary cost.