With a 233mhz, certain games are bound to run slower, like anything using color arithmetic (when they do effects to simulate translucent water or fog) or any special chips like super fx, sa-1, sdd1, etc.
Anyways, you also may want to try an OLDER version of ZSNES. Like around 0.7XX. As it got newer it got slower. Btw sound may not be playing because I believe sound emulation output may be disabled by default.