It seems to work like this:

use Text::Balanced qw(extract_bracketed);

my $string = "Param1(x,y,z), Param2(1,2,3), Param3(a,b,c)";
print "Original string: ", $string,  "\n";

my ($ext,$rem,$pre) = extract_bracketed($string, '()', '[^(]*');
print "extracted: $ext\n";
print "remainder: $rem\n";
print "prefix:    $pre\n";
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All I've really changed is the prefix regex. I'm now saying that the prefix is one or more non-bracket characters. I'm a little confused tho' - I'd expect that to be the default behaviour.