LGT CREW RPT OF ABNORMAL ATC HANDLING PROCS WHILE INBOUND FOR IAP ILS APCH.

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ON APCH INTO BNA; CLRED TO 2300 FT MSL ON A HDG OF APPROX 230 DEGS TO INTERCEPT THE 20L LOC. 170 KTS. BEFORE INTERCEPTING THE GS; THE APCH CTLR GAVE US A HDG TO THE SSE; OFF THE LOC IN ORDER TO GET SPACING ON THE ACFT SHOOTING THE APCH IN FRONT OF US. THIS WAS FOLLOWED BY A NUMBER OF INSTRUCTIONS TO TURN TO DIFFERENT HDGS DURING A SHORT PERIOD OF TIME. ALSO IN THIS NUMBER OF EXCHANGES; I EITHER ASKED ABOUT OUR ALT OR WAS GIVEN A CLB TO 3300 FT BY THE APCH CTLR; WHICH CONFORMED WITH THE MINIMUM SAFE ALT. ALL THIS WAS FOLLOWED BY THE INSTRUCTION TO IMMEDIATELY TURN APPROX 180 DEGS FROM OUR HDG. AT THIS POINT; I WAS OVERWHELMED AND ASKED THE APCH CTLR WHAT HE WAS DOING TO US. ANOTHER CTLR CAME ON THE RADIO AND ASKED WHAT OUR ALT WAS -- I RESPONDED CLRED TO 3300 FT WHICH IS WHAT WE WERE DOING. HE STATED THAT THERE HAD BEEN A MISCOM ABOUT OUR ALT AND PROCEEDED TO VECTOR US AROUND FOR ANOTHER ILS TO RWY 20L. LANDED WITHOUT FURTHER INCIDENT. BOTH THE CTLR AND THE CREW HAD A VERY HIGH WORKLOAD. AT TIMES LIKE THIS IT IS EXTREMELY IMPORTANT FOR BOTH PARTIES TO BE PRECISE AND CLR IN ALL RADIO XMISSIONS. IN OTHER WORDS; PROFESSIONAL. HAD WE BEEN BETTER INFORMED AS TO THE TFC SIT AND THE CTLR'S PLANS; WE MIGHT HAVE BEEN ABLE TO ASSIST IN PREVENTING ANY MISCOM. TCASII; WHICH WAS ON BOARD AND OPERATIONAL; WAS IN THE 30 MI RANGE; WHICH IS THE LOWEST SCALE ALLOWED WITH THE RADAR ON; WAS OF LITTLE HELP BECAUSE OF THE NUMBER OF ACFT IN A RELATIVELY SMALL AREA. IT IS VERY DIFFICULT TO ACCURATELY ASSESS SPACING IN THE TERMINAL AREA ON THE 30 MI SCALE.