The IRX files in my experience have largely been Device drivers. USBD.IRX, for example, is used to interface with a USB device.
If that's a full file listing, then you might have to dig around a little deeper, since it would seem that all of the necessary in-game assets would likely be squashed into the largest file there. If that's the case, you'll have to find out if there's a file extractor online to help you get at the chewy bits.
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