ACR X NON ADHERENCE TO ATC INSTRUCTIONS AFTER GAR HAD CONFLICT WITH Y.

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ACR X FOLLOWING AN ACFT TO RWY 32 AT PIT. OUR SPACING WAS ABOUT 25 MI WHEN WE WERE CLRED TO LAND. THE COMMUTER AHEAD OF US WAS CLRED TO EXIT THE RWY AS QUICKLY AS POSSIBLE. HOWEVER; THEY WERE SLOW TO EXIT AND I DECIDED TO HAVE THE FO EXECUTE A MISSED APCH. AS WE WERE EXECUTING THE MISSED APCH; WE WERE UNABLE TO COM WITH PIT TWR DUE TO FREQ CONGESTION. PIT WAS USING ALL 3 RWYS FOR TKOF AND LNDG. THE TWR INITIATED CONTACT BY TELLING US TO MAKE A L TURN OVER THE TWR AND CLB TO 3000 FT. WE ANSWERED AND TWR AGAIN CONTINUED TO WORK OTHER TFC TYING UP THE RADIO. I ASKED 2 TIMES FOR A SPECIFIC HDG AND WAS UNABLE TO BREAK THROUGH THE RADIO CONGESTION. WE ASSUMED THE TWR WANTED A TURN TO ENTER DOWNWIND. THIS TURN PUT US ACROSS THE DEP END OF RWY 28L; WHICH HAD ACR Y CLBING OUT. I SAW Y AND DIRECTED THE FO TO TURN BACK R TO PARALLEL. WE ALSO HAD AN ACFT CLBING OUT ON RWY 28R. AT THIS TIME; THE TWR GAVE US A N HDG AND THEN IMMEDIATELY FOLLOWED WITH A S HDG. WE WERE NOT IN A NEAR MISS SIT BUT IT COULD HAVE BECOME ONE. THERE IS AN INHERENT PROB WITH USING 2 PARALLEL RWY AND AN INTERSECTING RWY AT THE SAME TIME. A GAR CREATES A POTENTIAL DANGEROUS SIT; COMPOUNDED BY HVY RADIO CONGESTION.