There is no where near enough info here to begin to figure this out. There have been some good tips and suggestions, but they may or may not work depending on the cause of the problem. We can't help you solve your problem without knowing what it actually is. The "treblely and tinny" sound is a symptom of something else, not the problem.
First -"What" mics are you using. The "vocal" mics could be SM 58s, not my first choice for kick and snare, but certainly shouldn't be a "problem". On the other hand, these could be some crap from Walmart....THAT would likely be a problem.
Second - As for phase issues, that's easy to check on the existing recorded tracks. Mute all but the kick (I assume the three drum mics went to individual tracks (not to be confused with inputs). Does that sound thin and tinny? If so, something else is going on, because with only one mic, there can be no phase issues.
Third - Are you recording with any EQ or filters on, rather than flat? It's OK to do so IF you know what you are doing. Do the input channels have LOW CUT filters on them, and are they engaged?
Fourth - Is it your playback system. Maybe your speakers are lying to you. What does everything else sound like? Print the drums to a CD (without your whacked out bass boosted EQ curve from Cubase) and listen elsewhere. Still thin?
If you can toss an example up on the web somewhere we could listen to, that would help.
FWIW - The drums here (
www.concrete-blues.com ) were done with 4 mics using the Glyn Johns method (Google it), with the addition of a spot mic on the snare.