NAD CD player won't play in NAD 3020 amp

Hello all - This is my first time on here, a Google search found you. I am not what you would call a professional audiophile at all so please speak in idiot speak. I have a NAD 5325 CD player I bought for $10 at Goodwill. My girlfriend recently bought me a NAD 3020 amp for my birthday, just like the one I used to have years ago and loved. My Technics SL1200 turntable sounds amazing through it, as does my Onkyo R1 cassette deck, but when I play my NAD CD player through either the auxiliary or tuner settings on the 3020 it sounds odd. There is no setting for CD on the front plate. This is an old amplifier. When I play a CD there is no vocal, and barely any music, just a wash of reverb, as though the song was playing at the other end of a long tunnel. A professional sound engineer pal of mine said I should switch the speaker cables around but that didn't work. I've tried all combinations of this and nothing brings the vocal in. What is going on please? I've never heard the like of this before. Thanks all.
Did you try the CD player in another system?
I think you might have a bad cd player. You know that the tape input works because you said the Onkyo cassette deck sounds okay. Try puting the cd player into the tape input using the same cable that hooks up the tape deck, (that will eliminate a bad cable). If it still sounds bad, your cd player is at fault.

The tuner, aux and tape inputs are all the same, so it really doesn't matter which one you use. The phono input is for turntables ONLY, do not use it for anything else.
I doubt it will fix your problem because you say that your other sources sound OK, but its worth a try. If your voices are not "locking in" as you say, you may have them wired out of phase. Go to 1 of your speakers and reverse the speaker cables at the binding post. Put the + where the - currently is and put the - where the + currently is. Do this on 1 speaker only and they play some music. If this fixes the problem, you will hear it immediately.

Also, you may want to have a look at your NAD. Its very common to find a solder connections go bad; usually around the RCA connectors.