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Looks like the company Paradigm Entertainment was using this MPK container format for other games as well, for example Mission: Impossible – Operation Surma is one of them. Both Xbox and PS2 versions have them.

I've tried Nova Software Extractor and Cube Media Player but they didn't pick anything up.
Couldn't even find any relevant info about the format.

MUSIC.MPK

Use the Advanced Cutter in VGMToolbox by selecting RIFF Style Header as the preset and select the MPK file as the file to search. After all of the .wavs are extracted, rename the extension to .xwav and you should be able to play them with vgmstream.

Many thanks. That did the trick.

Edit: Also just found out by advice from another forum that to get proper file names from MUSIC.MPK use Watto game extractor. Resulting WAVs still have to be renamed to .XWAV to be playable with vgmstream.