"I don't see anything online called Maqc ROM."
I think that was a typo. A PC graphics card can be converted to function in a Mac, after flashing its EEPROM chip with the specific Mac ROM code extracted from the Mac version of the card having the same GPU. It's not a one-size-fits-all situation. Ideally, the appropriate code needed for your (PC) Radeon HD5830 would need to have been extracted from a Mac Radeon HD5830, if one was ever produced. A modified, compatible code may have been created by the experts who routinely flash graphics cards.
Complicating matters, AMD licenses its technology to other electronics manufacturers to produce graphics cards with their GPU chipset. When I flashed ATI (acquired by AMD) Radeon graphics cards about 15 years ago, I used ATI's retail card. Some of the licensed, third-party manufacturers, like Sapphire, VisionTek, Diamond, etc., used a smaller capacity ROM chip that was adequate for the PC code, but wasn't capable of accommodating the larger Mac code. Again and in some cases, the flashing gurus were able to create a truncated Mac code to fit, but that's a task beyond the capability of the average user. I flashed my cards in a PC using DOS commands. The first part of the procedure was to extract and save the existing PC code, before proceeding to overwrite it with the Mac code. That was a safeguard in case something went wrong with the flashing. If you make a mistake in the flashing process, you could render the card useless.
I can understand your desire to use a card that you have, so if it's a suitable candidate to flash for use in your Intel-based Mac, you might consider paying for the flashing service that's found on the website that BDAqua provided. If you contact them, at least you can be advised of the expense and whether it's worth it.