ACR X TCASII RA WITH ACFT Y WHILE ON VISUAL APCH TO PARALLEL RWY.

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I WAS ON THE JUMPSEAT GIVING THE CAPT HIS ANNUAL LINE CHK DURING APCH TO DFW. VISUAL APCHS WERE BEING MADE TO RWY 17L AND 18R IN GOOD VISUAL CONDITIONS AND VECTORED TOWARD RWY 17L OFF BLUE RIDGE VOR ARR. VECTORS; SPD REDUCTIONS AND ALT CHANGES WERE ACCOMPLISHED. I SAW TFC ON A HIGH RWY 17L DOWNWIND GO OVERHEAD AND WE WERE GIVEN A R TURN TO 260 DEGS AT 230 KTS AND 3000 FT MSL. THE ARPT WAS IN SIGHT AND NUMEROUS ACFT WERE OBSERVED VISUALLY AND ON TCASII. APCH ASKED IF A SPECIFIC ACFT Y TO OUR L WAS IN SIGHT. THE CREW RESPONDED THEY WERE UNSURE OF THE SPECIFIC TFC. OUR FLT PATH CONTINUED TOWARD THE W. THE CREW WAS DISCUSSING TFC AND TRYING TO SORT OUT THE SIT WHILE I HEARD THE CTLR ASK IF WE HAD THE ARPT. I RELAYED THE RADIO CALL THE CREW HAD MISSED TO THE CREW AND THE CTLR AGAIN ASKED IF THEY HAD THE ARPT. THE CREW RESPONDED THEY HAD THE ARPT AND THE CTLR ORDERED AN 'IMMEDIATE' L TURN. DURING THE TURN; AN ACFT ON APCH RWY 18R BECAME A TCASII RA WITH 'MONITOR VERT SPD' WHICH THE CREW COMPLIED WITH. APCH GAVE US RWY 17R BECAUSE TWR SAW A PROB AND WE LANDED RWY 17R. THE CTLR SEEMED TO EXPECT AND NEED VISUAL CONTACT WITH A SPECIFIC ACFT. IDENT OF A SPECIFIC ACFT MAY BE DIFFICULT OR IMPOSSIBLE IN A CROWDED SKY. WE NEEDED VECTORS ON TO FINAL NOT AN INTERCEPT VECTOR SINCE CALLS ABOUT TFC WENT BACK AND FORTH SEVERAL TIMES; A RADIO CALL WAS MISSED AND WE EARNED A TCASII RA. I HAVE DEBRIEFED THIS WITH MY COMPANY AND THEY PLAYED BACK THE VOICE TAPES. A SUPVR SAID THE APCH HANDLING WAS 'SLOPPY.' THIS IS A REAL PROB IN DFW AND VECTORS N THE FINAL; THEN A VISUAL ARE NEEDED. THE CREW SHOULD HAVE VOLUNTEERED THAT THEY DIDN'T HAVE THE SPECIFIC TFC BUT DID HAVE THE ARPT. APCH COULD HAVE ASKED IF WE HAD THE ARPT AND POINTED OUT TFC LATER. CREWS ARE RELUCTANT TO ACCEPT A VISUAL IF THEY HAVE TO ASSUME SEPARATION FROM AN ACFT THEY ARE UNSURE OF.