What about connecting a switch to your wga600n gaming adapter which will give you more ports?
As far as the DAP-1522, you indicated you tried everything to set the adapter up. It would be helpful if you could detail the steps you followed so we can help trouble shoot. Also, do you want to connect at 2.4Ghz or 5Ghz? If you want to connect at 5Ghz you will need to give your router a different ssid for the 2.4Ghz band and a different ssid for the 5Ghz band. You can do this by selecting setup, then wireless settings, then scroll down and select manual wireless setup. Each channel (2.4, 5Ghz) will have a name and you need to give them different names. Once these changes are saved, you may need to log back into 192.188.0.1. Since you tried a bunch of things, try these steps:
(I have the dir-825 not exactly sure about the DIR-628)
1. I would first reset the adapter by putting a paper clip inside the hole under the reset on the back of the adapter.
2. Then try setting the DAP-1522 to auto mode.
3. Then I would go into your router (dir-628) web page by typing 192.168.0.1 and under advanced tab, look for a tab called wifi-protected setup and click on that. Scroll down the settings page and look for a button that says Add wirless device with wps.
4. Then select auto button, which brings you to another page, and select pbc, press the button on the side of the dap-1522 and make sure the button starts to blink blue, and then select connect on the same page you selected pbc. Once the devices are connected, the blue light stops flashing.
5. Then you can go into the adapter browser settings page by typing dlinkap. There you can choose the 5Ghz band by launching wireless wizard, give the device a name (if you change this from dlinkap, you will have to type that name next time you log into web settings interface instead of dlinkap, change this name if you plan on adding more adapters in the future). Click next, then next again, then select manual configuration, then choose site survey and choose the ssid that contains the name of your 5Ghz band.
There are a bunch of other configuirations, but for now this should get you started.
It was a royal pain to get my dap-1522 setup, but now it is working well. Most of the reason it was a pain was I didn't know about how to use all the different settings.