The only 500 unit that will work is a 568.2 that has been upgraded or a 568mm, both having the MHR connection. You will see the MM's come up, though prices seem to vary greatly on them.

MHR

CJ

Primary: MD600, MS200 (SpeakerLink to AES), Trinnov ST-2, Ayre V6-xe, Salk SS8 3x LRC.
Secondary: MC600 (whole house).
Zone one: 568.2, G57, MS200, Spatial Hologram M2SE.
Zone 2-6 (Awaiting assignment).