A CL-600 FLIGHT CREW EXPERIENCED EICAS MESSAGES STAB TRIM; MACH TRIM; AND AUTOPILOT TRIM. THEY DECLARED AN EMERGENCY AND RETURNED TO THEIR DEPARTURE AIRPORT.

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AT 13000 FT CRUISE FLT CAPT AND I ENCOUNTERED A STABILIZER TRIM; MACH TRIM; AND AUTOPLT PITCH TRIM CAUTION MESSAGE IN OUR EICAS SCREEN. THIS LEAD TO HAND FLYING THE AIRPLANE IN A NO TRIM SITUATION. BECAUSE EXTRA FORCE WAS REQUIRED TO FLY THE AIRPLANE WE DECLARED AN EMER; RUNNING THE COMPANY FLT MANUAL INSTRUCTIONS ON EACH OF THE ITEMS; BRIEFING OUR FLT ATTENDANT AND RETURNING TO THE GATE AT ZZZ WITHOUT FURTHER INCIDENT. OUR OTHER MEL'S AT THE TIME WERE AN IDE #1; RTU #2 (COM); NAV LIGHT; AND DOME LIGHT. ALL ARE ACCEPTABLE TO FLY WITH ACCORDING TO OUR MEL MANUAL. UPON LNDG WE CHANGED ACFT AND DEPARTED SHORTLY AFTER IN A DIFFERENT ACFT. LATER; I DID INFORM MY SUPVRS THE ITEMS WOULD NEED TO BE REPAIRED AND CLRED BEFORE I WOULD FEEL COMFORTABLE FLYING THE ACFT AGAIN. IT IS MY UNDERSTANDING THAT REPAIRS WERE MADE THAT EVENING. I DO NOT KNOW WHAT LEAD TO THIS PARTICULAR SYSTEM FAILURE BUT THE COLLECTION OF MEL'S MAY HAVE PLAYED A PART. IT IS MY BELIEF THAT ITEMS SHOULD BE CLRED/REPAIRED IN A TIMELY MANNER. IN THE FUTURE; IF NUMEROUS MEL'S ARE ENCOUNTERED ON AN ACFT AT A SINGLE TIME; THEN I BELIEVE I SHOULD DISCUSS THE SITUATION WITH MY SUPVR AND IF NEED BE; DECLINE THE FLT.