Since you say you love the sound of your NAD with the CD player connected directly but need a way to control volume, I strongly recommend you try a passive preamp. In all likelihood, it will preserve that sound you love better than any active preamp unless you spend obscene money. I'd look at this:
http://www.tortugaaudio.com/products/ldrx-passive-preamp/
30 day in-home trial with full refund if not satisfied. Don't listen to the passive pre naysayers, just give it a try and see what you think.
http://www.tortugaaudio.com/products/ldrx-passive-preamp/
30 day in-home trial with full refund if not satisfied. Don't listen to the passive pre naysayers, just give it a try and see what you think.