When you say 'screen,' do you mean pop filter? Or the large foam windscreen that often comes with mics? DO NOT use the large foam windscreen unless you're outside (and then, you should probably choose a different mic).
Secondly, consider your distance from the mic. If the mic is in cardioid pattern (as it often is for lead vocal tracks) then it will be subject to proximity effect, which means that the closer you get to the mic, the more exaggerated (and artificial) the low-end response will become. Cardioid is common as it gives a solid weight to the track and reduces ambient information, but you might benefit from backing up a foot or even more to lighten and better balance the track. You could also try omni pattern for a different perspective. Sounds like your room is damped, so it may still result in a rather dry sound for you to mix later.
Thirdly, with respect to your reference to 'professional vocals,' which I take it means commercial releases, keep in mind that they likely were not only tracked well, but processed well too. Many common vocal processors (like an LA-2A) will add a certain harmonic content that makes the sound richer, silkier, edgier, whatever, not to mention EQ used to remove the cloudiness and increase the clarity of the track. Not all of that was achieved at the tracking, though proper tracking is critical. I recommend you get as close to the sound you're wanting with mic selection and placement. You can worry about the other stuff later.
Lastly, the room you're in, so much as it has been effectively removed from the equation by means of padding and the use of a directional pattern on your mic, isn't really going to impede your ability to capture a great vocal tone, so I wouldn't worry too much about that.
I'd first try varying your distance from the mic. Don't be concerned that you're backing off more than you think you should. Try it anyway. Some of the most appropriate vocal tones I've captured were as much as 2 feet-ish from the mic (works well for background/stacked vocals too)! Then if it still feels too dull, you might audition some other mics. The preamp you're using is pretty much a clean device, and while it's not the kind to add silk and sheen, it certainly isn't contributing to the dullness.
Hope this helps!