Do I really need a preamp?

Of what quality is the variable output device on the CD? Usually they are around the same quality/sound as a Radio Shack Receiver! Also the variable out may or may not have the ability to drive your amp. It may sound "ok" but you'd have to try it to see if it meets your requirements. But if sound IS ok then no reason not to.
A passive (high quality) volume control is another option from the full output jacks on your CD.

You should check out a passive unit, it will add almost nothing to the sound but will add the source switching you need. Check out the kit from http://www.welbornelabs.com

You don't have to have a pre-amp with a variable output digital system. Alot of people think it's best not to add another layer of curcuit into the chain. I have done it both ways and tend to like what a pre-amp adds to the sound. I realize I'm adding something and in the best systems that's bad, but in the systems I can afford I feel it sounds better with a pre-amp. I use a tube pre with a solid state amp, I think the tube adds some warmth and sounds less digitial. I would suggest trying a pre-amp for a week-end if possible and switching back and forth. As far as hooking up both I don't know the right way, I can imagin some set-up but I will leave that one to others. J.D.

I played around with the variable connection out of the Levisnon 39 and passive preamps. To really get the max out of your speakers (especially if they are dynamic speakers) you will always need a good active preamp for the dynamics and soundstage. Also, good power cords like the maganan reference and whale elite add to it. That's a whole other forum discussion. There are no short cuts at this level in hi-end audio.

Although off topic a bit, in my opinion anything that you add will color the sound. It just depends if you like the way the end result sounds. I find it that way for interconnects speaker cable, digital cable, power cords, amp, preamp, changing tubes, etc. Some are more transparent; some sound better, all color to varying degrees.