I am running 2 converters, a MOTU 2408, and a MOTU 2408 MKII. For the purposes of leveling I a generating a 1k tone at 0dB out of my RME sound card via light pipe. That is goes to my 2408, which converts it to analog. The analog signal then goes directly to my 2408 MKII which is sent via light pipe back to my sound card. When the signal leaves it is at 0dB, when it returns it is at -6dB. Where do the 6 dB go to?