If you talk about same manufacturing date, i dont think thats necessary, it will be difficult otherwise. Even same batch sometime have slight performance variation. but if you can afford, why not? That should be better or lesser variation. Since cost is not an issue, you should stick to one type mosfet/part number and install all new, the older working fet you can keep as backup spare. When installing, you can install 1 mosfet 1st for each side and test at lower power sound volume. If everything ok, install all 3 mosfets for each side for full operation. current limit Psu may also help to see current consumption during idle. 0.3 to less than 1A idle current should be normal. Ymmv.