C.d player with built in Pre amps i.e Wadia

Volume control is via the analog outs of the cdp, not the digital out. In any event, I have the Opus 21 and, in my system, I strongly prefer using a separate preamp. However, this is a personal preference thing and largely system dependent, I suppose. You will only know what's best in your system by trying it both ways.

To clarify my prior response, I have the GNSC modded Opus 21 as well and its a wonderful CDP. When I first got it, I used it as a pre and it did an admirable job; however, inserting a pre into my system really allowed the Opus to do its job as a CDP. The sound stage opened up, etc. Again, this is all system dependent. You have to consider input/output impedences, gain requirements, etc., just as you would in selecting any pre. In MY system a separate pre works better. In yours, using a CDP as your pre may work wonderfully. You will just have to experiment.