Understood.
I'm running out of ideas now, have to think it's either driver related, or an issue with the motherboard.
One thing you could try. Is buy a sound card, and disable the on-board in the bios. The quality of on-board is not great even when it's working.
For example I use Asus Essence ST and Essence STX II sound cards - the difference in audio quality compared to onboard, it's like comparing £20 dac, compared to £500 separates CD player.
I guess since the microphones are USB, I would need an adaptor from USB to jack for these sound cards to work right?