The reason that the SP 1200 sounds like it does is because it is only sampling at a 22khz rate and is only 12 bit. Also the sample time was only 10 seconds. This was (and is) great for doing hip hop drums and samples to give it that "dirty drums" sound. Most of the hip hop producers that used the SP 1200 were getting there samples from wax which added more to the "dirty drum" sound because of the added crackle and pop that wax gives you. The MPC 3000 samples at a much higher frequency of 44.1 khz and is also 16 bit which is basically CD quality. If you tweak your samples in the MP you can get them to sound dirty, but there is no tweaking necessary for the SP 1200. The SP 1200 is giving you all it can give, and its best and clearest sample will always be "dirty", and thats great if thats the only drum sounds that you want. If you however need to use some super clean and crisp drum sounds (for some RnB for instance), then the SP 1200 probably isn't the machine for you.
http://www.vintagesynth.com/ If you go to this link and punch in SP 1200 in the search box, the first link that appears will tell you all about the specs on the SP 1200. You can do the same for the MPC.