dBpoweramp Music Converter

The examples I've found for coreconverter.exe show that it apparently expects the quoting on the values of the options, not over the entire options, which may explain why it's having trouble parsing the option string, since the default behavior of Win32::ShellQuote as used by IPC::Run3 is to produce option strings that look like ... "-outfile=nul" "-convert_to=wave" .... Although this is not the prettiest solution, you might try something like the following (I obviously can't fully test this since I don't have dBpoweramp).

use warnings;
use strict;
BEGIN { $ENV{IPCRUN3DEBUG} = 1 }
use IPC::Run3 'run3';
use Win32::ShellQuote qw/quote_system_string/;

my $filepath = shift;
my $command = join ' ', 
    quote_system_string("C:\\Program Files\\dBpoweramp\\coreconverter.
+exe"),
    "-outfile=".quote_system_string("nul"),
    "-convert_to=".quote_system_string("wave"),
    "-errorfile=".quote_system_string("core.err"),
    "-infile=".quote_system_string($filepath);
run3 $command;
[download]

The command run will look like this, which I think has a better chance of working: "C:\Program Files\dBpoweramp\coreconverter.exe" -outfile="nul" -convert_to="wave" -errorfile="core.err" -infile="C:\Temp\Foo Bar"

By the way, have you looked at FFmpeg?