Are you asking, whether your CD player, DAC or receiver is actually converting the signal to analog? Or do you think that each one is doing the same thing in series? With each contributing to a refinement of the signal
Well to my knowledge it doesn't work as a series. The CD player will make the signal analog unless you bypass it's DAC and use digital outs. The DAC will not take an analog signal and convert it to digital then back to analog unless it specifically is capable of doing that. Instead I think it will just pass the analog signal along perhaps?? The analog/output stage of the DAC might get involved but I doubt it. The reciever will accept the analog signal as well and not convert it again, but, in this case the analog output stage will be involved in handling the signal and will matter in the final sound.
To answer your question the CD player.
If you are asking what you should invest in for upgrading. I think the one box CD player with the best transport mechanism, DAC and analog stage you can afford is the way to go.