I just scanned the ([Link: 129.33.22.12]) operating instructions manual, and as Akirby suspected, these devices support 2 IR addresses. The instructions to change the IR code are on page 36 (Using the Preferences Menu > Remote Control Code). Decide which one to change, then follow Akirby's instructions above.

PS: It's the 890 Pro user manual that mentions the RF Wireless Extender can have its ports addressed to allows a single port on an extender to control a device independently from the other ports. This allows multiple identical devices to be controlled independently. However, the 890 manual does not mention this capability. You can download the 890 and 890 Pro user manuals from these sites:
[Link: images.harmonyremote.com]
[Link: images.harmonyremote.com]