Good tube pre amp for a mostly digital system

I am seeking advice from the a'gon community concerning a tube pre for my digital system. Some folks have qued be in to the fact that adding a pre tube will do wonders for my sound.

I have the jeff rowland 501 mono's and the bel canto dac3 as a my pre, a marantz running as a transport. On thing about the rowlands is that they prefer balanced so the tube pre must have balanced outs.

I've looked at the valve audio black widow, the cary slp 05, and the aesthetix calypso. All have balanced outs, well I'm not sure about the valve audio. Any other recommendations? Is adding a tube pre really going to do anything for my sound?

Lastly, being lacking some knowledge in this world, I am confused as to how, if I got a pre amp, I would go about connecting my cd running digitally to my dac then to the pre amp. Would it just be a matter of connecting the dac to the pre or does the cd player also have to be connected to the pre amp?

Lots of questions I know, yet lots to learn! Any help, suggestions, opinions are be welcome.