One way is to use it as an wireless access point. In this case your cisco will be handling the routing.
Connect to cisco
1. Disable wireless on the Cisco DPQ3925
Connect to ENGENIUS
1. Change your router LAN IP to something other than 192.168.0.1
2. Log in again using the new IP.
3.Disable DHCP on the Engenius
4.Connect the Cisco DPQ3925 to one of the ENGENIUS LAN ports(leaving the ENGENIUS WAN port free). You will be able to connect your wireless clients to your new router.
What problem you encounter when you set up cisco as a bridge? Can elaborate? How did you do the bridging set up?
First how to secure the wireless network of engenius.
1. Connect to your Laptop to engenius using a cable.
2. Log on to 192.168.0.1
3. Go to wireless tab.
4. Click on the Security
5. Under encryption select WPA pre-shared key.
6. Click WPA2(AES) on the TAB below. This is the best best recommended option if all your device supports it. If you have any old devices that don't support it choose WPA2MIXED. Enter your desired wifi password.
7. Click apply. Your wireless engenius will be secure now.
Now how to do bridging.
1. Go to LAN tab
2. Under LAN IP change the 192.168.0.2
3. Click apply.
4. Wait to apply the settings then log onto 192.168.0.2
5. Go to internet TAB and make sure Dynamic IP address is there in Attain IP protocol.
Now connect your laptop to Cisco LAN port. Disable wireless under wireless settings (I guess you already know the IP is 192.168.0.1). Now enable the bridge only option in cisco. Your cisco will restart. Check your laptop IP address after restart. If it is some this that does not start witn 192. then bridging is done. Now you plug out your laptop and plug your engenius WAN port to Cisco LAN port. Restart your cisco. Connect laptop to engenius wireless. You must only connect your engenius to the cisco. No other device can be connectted to it.
You can connect all devices to your engenius either by wire or wirelessly. But don't connect any to your cisco other than the engenius WAN cable. As for channel it is recommended to use channel 1,6 or 11 as those are non overlapping channels. But if there are a lot of people using that channel in your area then that is of no use. You can check this using inSSIDer(Google it for windows or go to google play to install it on your android phone) and choose the least used channel in the locations that you will use WiFI. For antenna you can try as it depends on the interference. But if you are getting from ebay some of the gains described are inflated and the performance might be poor than the original ones.