To get serious dubstep sounds you're going to want to do a lot of EQing and sound shaping, very rarely will a sample sound passable as is.
Generally to get a good wubsteppy sound you'll want to boost the middle frequencies quite a bit of the sound, especially on the snare:
Example:
-Snare taken from the pendulum pack
http://www.mediafire.com/?nzl633kv2n9hqnm <- Sound as is
http://www.mediafire.com/?4c4r7chslmojyrc <- Middle frequencies boosted
Notice how it has a bit punchier, bit lower sound like most brostep snares tend to have?
Obviously it's going to take a little more work then that but that's the first step on the way there.
Other things to think about:
-Layering - this is one of the most useful things to do when forming drum sounds, basically piecing it together like a puzzle find the parts of different drum sounds that you like, EQ out the rest of the sound and then layer them over each other. While most sounds sound fairly weak on their own as a whole, most will have at least one part that they excel at (depending on where you get them from) - combining them in this fashion can you get you full powerful sounds if you piece everything together appropriately.
--It's a fairly common dubstep technique to layer a clap's upper frequencies over your snare to get a bit more pop to it. Just an example of the way this sort of thing can work
-Reverb - dubstep's pretty notorious for having a big airy sound to it, even in brostep the buildups tend to have a really open and reverby soundscapes. I'd suggest using an FX send for this sort of thing, busing the sounds to an auxiliary track where you EQ out the lower frequencies (bass sounds don't mix well with reverb) and run it through some verb. This way you can control how wet/dry the sounds are simply by how much you bus to the send, and it has your whole track running off a single reverb effect, saving some processing.
-Leave room for subbass - subbass is like the soul of dubstep, the last thing you want is your kick clouding out your wobbles subs. You can have the lower frequencies in the lighter areas, but it'll be to your best inteest to EQ out the lowest frequencies on your kick when the wobble bass comes in.
All in all the best advice I can give you though is
don't try to be Tomb,
be you - make your own style, make your own drums. Worship over a particular artist's sounds is never healthy for artistic development and then what happens should you actually succeed in recreating "his" drums? The novelty of the style is gone. Forge your own sound, don't obsess over someone else's - take inspiration, not total emulation.