One thing to check is that both are set to be slave and not master. A "normal" pair is one master and one slave. But in a surround situation the centre is normally the master and all other speakers are slaves.

hope this helps,

Chris

Lounge/Cinema, Trinnov, DSP8000XE, 4x 320.2 in-ceiling, M6 rear, 2x DSW.2
Roon Nucleus+ and 320.2 in-ceiling in many rooms (KEF in-ceiling in bathrooms)
Spare: DSP5000, 598, 562v2, 500Mk2, 518, 519, 504, 101B, M3, 861v4, 800 DVD, MS600, MC200