It's not the limitation of your turntable. But it is the limitations of something else you are using like maybe a phono preamp, software, and so forth. Are you getting this distortion just playing LPs alone through your stereo system or is it a product of converting to digital? BTW, you're not using a cheap turntable for your type of project. You would have been just as better served using a cheap Audio-Technica AT-PL50 or its rebadged TEAC P-A688. Also, Radio Shack sells the same turntable under its own badge. Don't laugh. This cheapo gets the job done.

Recheck the cartridge alignment and tonearm set up.

http://www.audiophilia.com/features/cartridge_setup.htm

Sanford & Son are here to serve. BTW, you have a good turntable. No need to upgrade to a Shure.