The 890 PRO can be used with up to 6 Harmony extenders (as mentioned in its user manual), but I don't know if the regular 890 (non-pro) can be used with more than one Harmony extender (its user manual does not mention multiple extender). Post #4 of this thread says it can: [Link: remotecentral.com] Also see post #3 of this thread: [Link: remotecentral.com]
