From my experience with the 876W and even the wireless module that goes into an 1800 or 2800 ISR, these wireless APs DO NOT do roaming and are assumed to be use for small/home office environments. Essentially, since you are using EAP, this adds more latency on the authentication process. Everytime a client, connects to an AP, it will go through that process. If the client roams around and trys to connect to the 876W as closest node on the WLAN, it would then have to reauthenticate because the 876W thinks it is the only AP on the LAN.
With the other APs, I assume they are IOS APs. Just make sure you have WDS configured and the WDS Manager will then act as the "key manager" and knows of the other wireless APs on the LAN. This guarantees a 150ms roam and manages clients more efficiently.
Again, to my knowledge, the 876W or any wireless module in an ISR router, is NOT capable or roaming.