the settings on the deck (-18, -12, -6, and 0dB) are gain settings, not an attenuator setting. so it's best to set it as low as possible that will still give you good levels. So I'd start with the deck at -18dB and no pad on your mic. personally, I always run my deck at the -18dB setting, and I also always use the -15dB pad on my mics. However, I think the beyerdynamic mics are more sensitive than the LSD2, so you might not need to use the pad on your mics.