Is this the same system you had your previous Music Creator working well on? Were you using the computer's stock sound card in that system?
Click P on the computer keyboard and list what your settings are there, especially under Audio>Driver Settings.
You can adjust the mixing latency more to the Fast side, but going too far will introduce pops, clicks and other audio glitches, possibly even audio dropout.
An audio interface that supports true ASIO drivers is the solution if you're unable to get satisfactory performance from your RealTek.