Aside from the ability to add some gain, I really don't feel that the 518 will bring much to the table when connected to the 568.2mm. Louder is not better. The 568.2mm is a very capable DAC and processor.

www.cmbintegrations.com
One step from the Presidency
#1 Trinnov Altitude 32-8-16, 271, 8000XE, 7200SEHC, 7200.2, Seaton F18, JL Fathom F113, Revel w990's, Kef R7, ATI 528 Amp, JVC RS4100K, SI screen. Roon Nucleus+, Eno AG, Eno M link, 218.
#2 Mark Levinson No5105, Ayre VX8 and CX8, Vandersteen Treo CT, Preamp varies.
#3 Meridian Ellipse