I went on a tube-pre frenzy and picked up a few including the Presonus. I'm still figuring out what's good for what, but here's what I found FWIW:
Presonus Tube Pre: easy to pick one up cheap. It seems to stay on the subtle side with the color (added tube drive, because that's what these do). Good for improving a scratchy cheap mic. Solid extras like pad and hi-pass. Balanced XLR out, but no 1/4" balanced out

A great starting point.
Studio Projects VTB-1: My favorite for direct bass. Keep it mostly SS and a little tube (about 9 o'clock on the mix knob). Can really capture a clean, round tone that hangs together. It can also be fuzzy if you dial in too much tube (which can be useful, too). Good for spicing up a thin voice. And lots of features including the regulars plus a polarity switch and 2 resistance settings(!) for whenever you want to break out that Royer R-121. Completely balanced in and out.
ART TubeFire: this is an 8 channel firewire interface that can also be used as 8 stand-alone preamps. Like all of these, the tube can be dialed in to taste, and that taste is tasty enough to make it my main tracking ins. The instrument in is great for guitar, as it doesn't choke the hiZ signal, and it seems to be easier to adjust its "tubyness" (tubeeness?), i.e. it's easier than the others to hear how hard the signal slams the tube and adjust what's happening to your signal.
This is more than it sounds like you want, though.
I always try to use TRS balanced 1/4" out into a line-level balanced in. You can go XLR out, but chances are you're just heading back into another pre, which you shouldn't need at that point.
If you're looking for tube sound for specific things, you might look at tube condensers. My favorite vocal set up right now is
a Sputnik into a plain ol' solid state Firebox.