It is possible as you would run the left/right SpeakerLink out of the 861 into the SpeakerLink input of the 818v3 and then the 818v3 SpeakerLink outs on to the front left and right speakers.
This configuration requires a discrete configurations to be loaded into the 861 and the 818v3.

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#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